FFECT OF DIETARY FAT AND PROTEIN ON MILK PRODUCTION,
MILK COMPOSITION AND NUTRIENT UTILIZATION
BY HOLSTEIN COWS
by
Aimé Joseph NIANOGO
ATHENS,
GEORGIA USA
1988

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AIME JOSEPH NIANOGO
Effect of dietary fat and prote in on milk production, milk
composition and nutrient utilization by Holstein cows
(Under the direction of HENRY E. AMOS)
Four trials were conducted to assess the effect of
dietary lipids on the performance of lactating Holstein
cows.
Trial 1 included 24 cows in early lactation fed 0 (C)
or 4% of the DM as fat (F) supplemented with either corn
(Zea mays L.) or soybean meal (SBM) for 56 d.
In trial 2,
12 cows in mid-lactation were used in a replicated 3 x 3
latin square: cows were fed either C or F and were
supplemented with either low or high level of rumen escape
protein (REP).
In trial 3, 12 summer calving (SC) and 12
fall calving (FC) cows were fed wheat (Triticum aestivum L.)
silage and either C or 1 kg Fat/d
supplemented with high or
low REP.
Cows were placed on treatment 1 d postpartum for
16 wk.
Trial 4 included 4 cows in late lactation in a
reversaI study with two 21-d periods and 2 levels of fat.
Cows were subsequently slaughtered and mammary tissue slices
were incubated with 14c-Iabelled L-Ieucine, L-Iysine, L-
phenylalanine or L-methionine.
In trial 1, milk yield of cows fed C and corn was lower
than other groups.
Cows fed F and SBM had a greater milk
fat yield than those fed F plus corn.
Fat decreased
efficiency of milk protein production.
In trial 2 intake of
DM, digestibility of fiber, milk yield and milk fat were
decreased by fat. Efficiency of milk CP production was
increased with low protein high REP diets.
Results suggest
that when fed diets high in REP, cows in mid lactation may

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require less CP than the amount recommended by the NRC.
In
trial 3, digestibility of DM and fiber were increased by
fat.
Fall calving cows produced more milk fat, SNF and
protein than SC cows.
Calving season had more effect than
level of fat or protein solubility.
In trial 4 dietary fat
increased plasma lipids and glucagon, decreased plasma
glucose and decreased amine acid uptake (21.2%).
Uptake was
highest for leucine and lowest for methionine. Results
suggest that dietary fat may decrease milk protein synthesis
by lowering the rate of amine acid uptake in mammary tissue.
INDEX WORDS:
Dietary Fat, Holstein Cows, Protein Level,
Rumen Escape protein, Amino Acid Uptake, Milk
Production, Milk Protein, Milk Composition.

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EFFECT OF DIETARY FAT AND PROTEIN ON MILK PRODUCTION,
MILK COMPOSITION AND NUTRIENT UTILIZATION
BY HOLSTEIN COWS
by
AIME JOSEPH NIANOGO
B.S., University of Ouagadougou, 1979
M.S., Tuskegee Institute, 1982
A Dissertation Submitted to the Graduate Faculty
of the University of Georgia in Partial Fulfillment
of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
ATHENS, GEORGIA
1988

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DEDICATION
To the Workers at Gampela, Burkina Faso, and to aIl
Sahelian Farmers
To Elizabeth my Mother, Fati my Aunt, Georgette my wife,
Edith, Isabelle, Olga, Stephanie and Rebecca my sisters,
and to African Women
To Willy, Rocky, Thiery, Louis and to Third World Children
To Courage, to Determination, and to Victory
iii

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EFFECT OF DIETARY FAT AND PROTEIN ON MILK PRODUCTION,
MILK COMPOSITION AND NUTRIENT UTILIZATION
BY HOLSTEIN COWS
by
AIME JOSEPH NIANOGO
Approved:
---,-ri,~.[;-wu.:.....;."7"f--/_t....;... ~"""-"-____
-.:;<&::....-
Date I()- 27-88
Major ~fessor
/Jnal~ t( ~tft;;/J
Chairman, Reading Committee
Approved:
Date

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ACKNOWLEDGEMENTS
The author wishes to extend his deep appreciation and
gratitude to Dr. Henry Amos for his determination, patience
and guidance. Gratitude is also extended to Mrs Amos, Dr Tom
Huber, Dr. Carl Hoveland, Dr Mark Froetschel, Dr. Milton
Neathery and Dr. David Spruill for their guidance and care.
A big hug to Mrs. and Dr. DarI Snyder, Bernadette
Allard, Sue Tweed, Eva Miller and to Edna Fisher for
multiple and multiform contributions.
Special thanks to my friends Clara Parker, Felicia
Kautz, Lynn Cathcart, and Diana Peters for their help in the
lab or at the dairy center, to Lisa Kriese, Andra Nelson and
Jerry Arnold for their help in the statistical analyses of
the data, and to Diane Anderson, Angela Martin, Karen
Houseknecht and Claudia Wiedwald for being around when l
needed them.
Special thanks to my long time friends Clarisse and
Louis Zouré, Jeanne and Paul Nyameogo, Henriette and
Evariste Yaogho, Odile and Idrissa Ousmane, Pierre Palo, and
Narcisse and Arsene Ouédraogo for their unconditional and
never ending support.
My deepest gratitude to the taxpayers of the United
States who provided financial support for my graduate
education, and to the people of Burkina Faso who provided
iv

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v
financial and moral support for my undergraduate and
graduate education.

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TABLE OF CONTENTS
DEDICATION. . . . • • . • . . . . . . . . . . . . . • . . . • • . • . . . . . . • . . . • •
i i i
ACmOWLEDGEMENTS. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • •
i v
INTRODUCTION. . • . . • • • • • • . . . . • • . • . • . • . . • • . . . . . • . . • . • .
1
REVIEW OF LITERATURE...............................
5
INFLUENCE OF LEVEL OF DIETARY FAT AND
PROTEIN ON MILK PRODUCTION, MILK
COMPOSITION AND RATION DIGESTIBILITY
(Manuscript prepared for submission to
Nutrition Reports International)
..••..•.•..•.
40
INFLUENCE OF TOASTED SOYBEAN MEAL IN
DIETS CONTAINING ADDED LIPIDS ON MILK
YIELD, MILK COMPOSITION AND EFFICIENCY
OF PRODUCTION (Manuscript prepared for
submission to Journal of Dairy Science).......
61
INFLUENCE OF DIETARY FAT, PROTEIN
SOLUBILITY AND CALVING SEASON ON
VOLUNTARY FEED INTAKE, NUTRIENT
DIGESTIBILITY, MILK YIELD AND
COMPOSITION (Manuscript prepared for
submission to Journal of Dairy Science)
90
vi

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vii
EFFECT OF DIETARY FAT ON L-LYSINE,
L-PHENYLALANINE, L-LEUCINE AND L-METHIONINE
UPTAKE BY BOVINE MAMMARY TISSUE IN VITRO
(Manuscript prepared for submission to
Journal of Dairy Science).....................
129
CONCLUSIONS. . • • . • • • . • • • • . • . . • . • . . • . . . • . . • • • . • • . . • . .
152

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INTRODUCTION
Milk production has been an area of active research,
particularly during the last 50 years. In the state of
Georgia alone, milk yield per cow has increased from 1279
kg/cow/year in 1925 to 5047 kg/cow/year in 1985 (Georgia
Crop Reporting Services, 1957; Georgia Agricultural
Statistics, 1986). Interestingly, while productivity has
increased, the number of cows being milked in Georgia has
declined sharply, from 354,000 in 1925 to 216,000 in 1960,
130,000 in 1980 and 117,000 in 1985 (Georgia Crop Reporting
Services, 1957, 1962; Georgia Agricultural Statistics,
1986). This allowed the state of Georgia to produce 30.42%
more milk with 66.95% less cows in 1985 than in 1925.
Such increases are due to progress in several areas,
including breed improvement, herd health, reproduction,
nutrition and management. The decrease in numbers may also
be an indication that land and other resources are more
limited, and that farmers are no longer able to accommodate
large numbers of herds. This trend is likely to continue and
will constitute an additional incentive for increased
productivity. A corollary to the increase in productivity is
that dairy cows are now extremely demanding in terms of
management, since several factors can affect milk yield and
composition.
1

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2
Milk yield is related to the ability of the lactating
dairy cow to consume large amounts of nutrients. However,
nutrient intake of dairy cows is affected by such factors as
diet composition, roughage to concentrate ratio,
physiological stage of the cow, environmental conditions
(temperature, air moisture, wind velocity), health, etc. In
order to achieve optimum milk output, producers need to have
as much knowledge and control of these factors as possible.
It is weIl established for instance that nutrient
requirements of dairy cows vary tremendously with stage of
lactation and stage of gestation. Nutrient density must
change, and feed composition needs to be readjusted
periodically during the lactation cycle.
Dairy cows in early lactation are in negative energy
balance, since nutrient output is greater than intake of
digestible nutrients. Ambient temperatures above 250 C are
common during the summer months in warmer climates; dry
matter intake of intensively managed cattle, including dairy
cows begins to decline between 25 and 27 0 C ambient
temperature (Beede and collier, 1986). The effects of heat
stress can be more or less severe depending on stage of
lactation. Feed ingredients yielding the highest amounts of
net energy for lactation (NEL) or metabolizable protein,
such as dietary fat and rumen escape proteins are
particularly appropriate during periods of physiological or
environmental stress.

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3
Feed ingredients are commonly available that can be
added to a ration in relatively small amounts to
substantially influence energy density or metabolizable
protein content. Hydrolyzed animal fat or soybean oil
provides 197.96% more NEL than does ground corn (NRC, 1988).
Common sources of protein such as soybean meal are actively
degraded by rumen microorganisms, producing useful microbial
protein but also high amounts of less useful ammonia. SBM is
65% degraded in the rumen, SBM heated at 140 0 C for 4 hours
is only 18% degraded in the rumen (NRC, 1988); Untreated
corn gluten meal is 45% degraded in the rumen (NRC, 1988).
Level and solubility of protein have direct influences on
amount of metabolizable protein available for absoption to
the host. Dietary fat, corn gluten meal, heated SBM and
other similar nutrients are however more expensive than
common feedstuffs and their inclusion in diets may not be
economically feasible in aIl situations.
Dietary fat has increased milk production and milk fat
test in several studies (Maynard et al, 1941; Palmquist and
Conrad, 1978). However, many negative effects have also been
reported, including decreased dry matter intake, decreased
fiber digestibility, decreased acetate: propionate ratio,
and decreased milk prote in content. There has been
significant progress in controlling fiber digestion with the
use of protected fat and calcium soaps (Palmquist et al,
1986). However, decreased milk protein remains a concern
because of the importance of casein and other milk proteins

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4
in cheese making (Dunkley et al, 1977). Milk protein is also
important for the survival and growth of newborn ruminants
raised on low quality pastures and in areas that are prone
to heat stress or droughts. Furthermore, human infants in
many areas of the world depend on milk prote in to satisfy
part of their daily prote in requirements. Therefore a need
exists to identify the mechanism by which dietary fat causes
milk prote in content to decline.
The objectives of this research were to investigate 1)
the effect of dietary fat on nutrient intake, nutrient
digestibility and nutrient utilization by lactating dairy
cows; 2) the importance of prote in nutrition (level and
source) on milk yield and composition in cows receiving fat
in their diet; 3) the effect of dietary fat on amino acid
metabolism in the mammary gland; 4) the effect of calving
season on milk production and composition.

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REVIEW OF LITERATURE
1) Effects of Lipids on Feed Intake, Rumen Metabolism
and Milk Production
la)
Introduction
Lipids are fO'..uct in all tissues,
in various forms and
concentrations. They serve roles ranging from major
structural elements of cell membranes to energy storage
forros in several plant and animal tissues.
Lipids also
participate in the metabolism of living organisms in the
forro of hormones, vitamins and bile salts (Vance,
1983).
ails are extracted from the seeds of plants which store
mostly triglycerides in their seeds. However,
only a dozen
plants with oil-bearing seeds are widely planted for the
purpose of oil production. There are several hundred more
varieties of plants with oil-bearing seedsi Butyrospermum
paradoxum is an example of a West African tree which produces
seeds that are used locally for the production of butter
(known as shea butter); parki~ biglobosa is another sahelian
tree that produces seeds containing 23% ether extract.
Th~se examples are an indication that oil-producing plants
are a resource whicll can be developed further.
Fu:=thermore
fats are a by-product of meat and fish processing plants.
Lipids have traditionally been used for human
consumption and for the production of detergents,
paints,
5

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6
lubricants, plastics, etc (Gurr, 1984). Documented research
on the nutritive value of fats for dairy cows May have
started in the 1900's (Palmquist and Jenkins, 1980a) and
gained renewed attention with the studies by Maynard and
coworkers (Maynard et al, 1941). These early studies
identified several effects of dietary fats, including
increases in the production of mi1k and milk fat. Further
studies have provided valuable information on the effects of
fat on feed intake, digestibility, and nutrient utilization.
lb) Some aspects of lipid digestion in the ruminant.
Ingested fats are hydrolyzed in the rumen by bacterial
enzymes to yield glycerol and long chain fatty acids (LCFA).
Glycerol is mostly converted to propionate. In contrast with
short chain FA's produced from microbial degradation of
carbohydrates, LCFA are not water soluble and are not
absorbed through the rumen wall. Long chain FA's increase
propionate production in the rumen, by inhibiting
methanogenesis (Chalupa, 1984). Unsaturated free LCFA May be
hydrogenated by several rumen bacterial strains (Kepler et
al, 1966; Kemp et al, 1975; Goering et al, 1977).
Biohydrogenation in the rumen causes absorbed FA to differ
in degree of saturation from ingested fats; this is a major
difference from monogastrics in which absorbed FA reflect
dietary FA composition.
Some FFA May be incorporated by rumen bacteria
(Emmanuel, 1978) and protozoa (Emmanuel, 1974; Demeyer et

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7
al, 1978; Girard and Hawke, 1978); this may allow greater
yield of YATP since energy originally directed to FA
synthesis is spared (Palmquist and Jenkins, 1980a). Rumen
microbes are dependent on yield of YATP for growth.
Lipids reaching the abomasum are dispersed into fine
emulsion particles as a result of abomasal contractions;
also contributing to the emulsification process are peptic
digests of dietary proteins, complex polysaccharides and
membrane-derived phospholipids (Carey et al, 1983). A small
portion of triglycerides are hydrolyzed by lipolytic enzymes
of the host animal in the abomasum (Carey et al, 1983).
Lipids entering the small intestine interact with bile
salts, dietary phospholipids and amphiphilic peptic digests
of dietary proteins to form finer emulsion particles.
Digestion of triglycerides and cholesterol esters,
absorption and transport of FA, monoglycerides and
cholesterol in the small intestine of the ruminant have been
described in several reviews (Carey et al, 1983; Palmquist
and Jenkins, 1980a).
Fatty acids are incorporated into triglycerides mostly
by the a-glycerophosphate pathway, with glucose serving as
the glycerol precursor, but also by the monoglyceride
pathway (Palmquist and Jenkins, 1980a). While FA of less
than 14 carbons enter the blood directly, triglycerides,
phospholipids, cholesterol and some mono- and diglycerides
are secreted into lymph vessels as lipoproteins (Palmquist
and Jenkins, 1980a).

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8
Feeding fat has increased blood total lipids in several
studies (palmquist and Moser, 1981; Palmquist and Conrad,
1978). Lipid components that are increased by fat feeding
include triglycerides, NEFA and cholesterol (Palmquist and
Conrad, 1978; smith et al, 1978; Rindsig and Shultz, 1974).
1c) Effect of lipids on dry matter intake and digestion of
fiber and other dietary components.
Dry matter intake: The effects of dietary fat on dry
matter intake (DMI) have not been consistent. Dry matter
intake has decreased with unprotected sources of fat (Storry
et al, 1977; Clapperton and Steele, 1983; Hawkins et al,
1985), and increased with unprotected ( MacLeod et al, 1977;
DePeters et al, 1987) and protected (Smith et al, 1978;
storry et al, 1977) lipids. There are also reports where DMI
was not affected by the addition of fat (Palmquist and
Conrad, 1980). It would appear that source and level of fat
and diet composition are determining factors in the
relationship between dietary fat and DMI. Although protected
sources of fat may be more readily accepted, it is not clear
whether the effect of fat on DMI is due to lack of
palatability of the fat or to a feedback effect of ingested
fats on voluntary intake. However, DMI needs to be
maintained at an adequate level for dietary fat to be of any
economic benefit.

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9
Milk fat depression and digestion of fiber: Although
adding fat to lactating cow diets provides preformed fatty
acids (FA) for milk fat production, dietary fat has often
caused milk fat content to decline (DePeters et al, 1987;
storry et al, 1974). Milk fat depression in cows that are
not fed fat is normally due to low roughage intake, and has
been attributed to a narrow acetate: propionate ratio (Van
Soest, 1963).
Similarly, feeding fat has resulted in a narrower
acetate: propionate ratio (Storry et al, 1974; Steele and
Moore, 1968; Nicholson and Sutton, 1971). In the case of fat
containing diets, it appears that acetate: propionate ratio
is lowered because of the negative effect of fat on fiber
digestion by rumen microorganisms (Lucas and Loosli, 1944;
Devendra and Lewis, 1974).
According to Devendra and Lewis (1974), LCFA may exert
a negative effect on fiber digestion by 1) physical coating
of the fiber by fat, protecting the fiber from digestion by
microbial enzymes; 2) a modification of the rumen microbial
population due to toxic effects of fat on certain
microorganisms; 3) inhibition of microbial activity from
surface-active effects of FA on cell membranes; 4) reduced
cation availability from formation of insoluble complexes
with LCFA.
It is now believed that rumen microbial activity is
inhibited, based on findings that FA inhibit rumen bacteria
in pure culture (Henderson, 1973). Free FA (FFA) are

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10
physically adsorbed cnte bacteria ( Hartfoot et al, 1974;
Henderson, 1973; Maxcy and DilI, 1967; Nieman, 1954). Short
chain fatty acids (SCFA) and unsaturated LCFA (ULCFA) have a
lower melting point and thus tend to increase membrane
fluidity. Decreased integrity of cell membrane may alter the
activity of a variety of membrane-bound enzymes. In tact,
bacteria survive slow changes in media temperature by
altering the activity of desaturases to change the ratio of
saturated FA to unsaturated FA in membrane phospholipids
(Quinn and Chapman, 1980). UFA are more inhibitory to
bacteria than saturated FA (Steele and Moore, 1968); and
SCFA are more inhibitory than LCFA (MacLeod and Buchanan-
Smith, 1972).
The inhibitory effect of fat on fiber digestion may be
reversed by fiber (El Hag and Miller, 1972), and by Ca
(White et al, 1958). If the level of dietary fat remains
constant, increasing the level of dietary fiber will cause
the inhibitory effect of lipids to be less efficient. Ca and
other divalent cations form insoluble soaps with FA,
therefore preventing FA from interfering with bacterial
membranes, and also liberates the fiber from any FA coat,
allowing its digestion by bacterial enzymes. One concern
with Ca soaps is that if calcium is in excess or if it is
absorbed inadequately, insoluble soaps may reform in the
large intestine and be excreted in the feces (Jenkins and
palmquist, 1984; Palmquist and Jenkins, 1980b). Dietary fat
has also been encapsulated in formaldehyde-treated proteins

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11
such as casein (Storry et al, 1974; Goering et al, 1977) and
soybean (Glycine max Terr) meal (Smith et al, 1977) to keep
the lipids from interfering with rumen metabolism; also,
ground soy flour has been protected using 5% formaldehyde
(Mattos and Pa1mquist, 1974).
Effect of fat on the digestion of nutrients other than
fiber: Nitrogen digestibility has increased (Lucas and
Loosli, 1944; Palmquist and Conrad, 1978; Pennington and
Davis, 1975; Swift et al,1947) or remained the same
(Palmquist and Conrad, 1978; palmquist and Conrad, 1980;
Depeters et al, 1987) with the addition of fat to lactation
diets. Digestion of ether extract increases significantly
with the addition of fat (Palmquist and Conrad, 1978;
Depeters et al, 1987). Digestion of gross energy May not be
affected by fat addition (Depeters et al, 1987). Digestion
of Ca and Mg has declined in some studies with the addition
of fat (DePeters et al, 1987). This may be consistent with
the findings that divalent cations form insoluble soaps with
fatty acids in the rumen (palmquist and Jenkins, 1980b;
DePeters et al, 1987) and in the large intestine (Grace and
Body, 1979). However, other reports have indicated no change
in digestion of Ca or Mg (Palmquist and Conrad, 1978).
1d) Effect of fat on milk yield and composition
Milk yield: Response in milk appears to vary with
source and level of fat and with stage of lactation. Yield
of milk and FCM in cows receiving fat have increased

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12
(Maynard and Loosli, 1944; Palmquist and Conrad, 1978;
DePeters et al, 1987), decreased (Palmquist and Conrad,
1980; Casper et al, 1988) or remained the same (Rindsig and
Shultz, 1974; Smith et al, 1978; Dunkley et al, 1977;
Palmquist and Moser, 1981; smith et al, 1987). However, it
does appear that when dry matter intake is not lowered, milk
production tends to increase. ~stergaard et al (1981) have
demonstrated the existence of a curvilinear response in milk
yield when increased amounts of dietary fat were fed. This
response is almost linear below an intake of 35 gm fat/kg
DM/day; increases in response are much less pronounced above
40 gm/kg DM/day. Furthermore, the response is greater in
early lactation and with higher yielding cows.
Effect on milk fat: Dietary fat has caused milk fat
content to decline (Depeters et al, 1987; storry et al,
1974a; Casper et al, 1988). This occurred mostly with
unprotected fats and in studies where fiber digestion was
altered; in such cases, the inhibition of de nove synthesis
exceeds the transfer of dietary FA into milk. Inhibition of
de nove FA synthesis may originate from a low supply of
substrates (acetate primarily), or from a negative feedback
effect of preformed lipids on acetyl-CoA carboxylase
activity. Dietary fat can also lower milk fat content by
increasing propionate production in the rumen; high
propionate causes a glucogenic response which increases
plasma insulin level; insulin inhibits the pituitary fat

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13
mobilization factor, and adipose tissue then competes with
the mammary gland for lipogenic substrates (McLymont and
Vallance, 1962). Growth hormone is now regarded as the
pituitary fat mobilization and is known to play a
significant role in nutrient partitioning to the mammary
gland.
In other studies, dietary fat has caused milk fat
content to increase, because of dietary FA transfer into
milk in the mammary gland (Maynard and Loosli, 1944; Storry
et al, 1974a; Dunkley et al, 1977; Smith et al, 1978;
Palmquist and Moser, 1981; Casper et al, 1988).
Smith et al
(1978) found that 25 to 35% of dietary FA may be transferred
to milk; de nove synthesis of FA in the mammary gland was
decreased 40 to 50% by protected tallow.
The FA composition of milk fat appears to be influenced
by dietary FA composition when protected fat is fed
(palmquist and Jenkins, 1980; Casper et al, 1988). Dunkley
et al (1977) found that aIl milk FA were decreased by
tallow, except C4:0, C16:1, C18:0 and C18:1. Feeding
protected safflower (carthamus tinctorius L.) oil increased
linoleic acid content in milk (Goering et al, 1976). Goering
et al (1977) found that soybean or cottonseed (Gossypium
hirsutum L.) oil UFA's increased the yield of linoleic acid
in milk only when protected from ruminaI fermentation; yield
of C18:0 and C18:1 was also increased, and compensatory
declines in milk C16:0 and C14:0 FA were observed. This was
thought to support biohydrogenation in the rumen (Goering et

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14
al, 1977). Smith et al (1978) reported that milk C6 to C12
FA declined with medium to high fat diets, whereas C4, C14
to C18 and UFA were higher in milk.
De nove synthesis of short and medium-chain FA other
than butyric acid is particularly inhibited by dietary fat.
This contributes to poor spreadability of the butter
(Dunkley et al, 1977; palmquist, 1984).
Milk fat of cows fed protected unsaturated LCFA such as
linoleic tends to rapidly develop an off flavor.
Polyunsaturated FA's are rapidly oxidized at the double bond
when exposed to air; Supplementation of the cow or addition
to the milk of antioxidants such as a-tocopherol acetate
prevents development of the oxidized off-flavor (Goering et
al, 1976).
Effect on non-fat milk components: milk protein seem to
be affected the most by dietary lipid supplementation. Milk
protein content or yield has often decreased with the
addition of fat; this topic will be discussed in relation to
protein metabolism in a separate section. Changes in lactose
and mineraI content have not been consistent enough to
create a concerne Effect on milk lactose appears to follow
the pattern for milk protein, to a certain extent. In a
study by DePeters et al (1987), both lactose and crude
protein (CP) content were lowered, and mineraI content was
increased by fat feeding. Dunkley et al (1977) found no
change in milk CP or lactose, using protected tallow.

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15
2) Protein Metabolism in Relation to Milk Composition
2a) Some aspects of the rumen metabolism of nitrogenous
compounds.
Under normal conditions, almost aIl non-prote in
nitrogen (NPN) and about 60% of dietary protein is degraded
by rumen microorganisms to produce ammonia, VFA and C02.
Some 40% of dietary protein reaches the abomasum undegraded
(Satter and Roffler, 1975) The majority of rumen bacteria
require ammonia as a nitrogen (N) source (Bryant and
Robinson, 1962). In addition to ammonia, bacteria utilize
VFA as carbon skeleton and energy in the form of ATP for
prote in synthesis. Protozoa participate in protein
metabolism by degrading a small amount of dietary protein
and by ingesting bacteria. However, microbial crude protein
synthesis depends primarily on bacteria (Owens and Bergen,
1983).
Activity of bacterial proteolytic enzymes appear to be
unlimited, and under normal circumstances growth of rumen
microorganisms produces significant amounts of microbial CP.
Satter and Slyter (1974) showed that the maximum N
requirement of rumen microorganisms can be met with 5 mg of
ammonia/dl ammonia. This is equivalent to about 13% CP in
the diet (Rofler and Satter, 1975). Ammonia in excess of 5
mg/dl is mostly absorbed through the rumen wall; a small
portion of plasma urea is recycled via the saliva or the
rumen wall, but under normal feeding conditions most of the
urea is lost in the urine.

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16
In practice, there are some advantages to this
situation. An important one for ruminants requiring more
than 13% CP is that the supply of CP can be arranged so that
diets effectively provide up.to 13% degradable CP; the rest
of the requirement may be supplied using protein sources
that are known to escape ruminaI degradation. Another
advantage is that aIl or part of the degradable protein
destined to satisfy the ammonia requirements of rumen
microorganisms may be replaced by NPN, as long as sufficient
energy is provided to maintain an adequate N: Energy
balance. Sources of NPN are in general readily degradable
and high losses of N in the urine occur when dietary total
digestible nutrients (TON) is low. Roffler and Satter (1975)
suggested that NPN is not useful in diets providing more
than 12% CP or less than 60 to 65% TON.
Prote in available for digestion and absorption by the
host animal is essentially the sum of microbial CP and
undegraded dietary protein and has been termed metabolizable
protein by Burroughs and coworkers (1972). The microbial CP
is believed to be of high but not ideal quality, varying
between 70 and 80% in biological value (Owens and Bergen,
1983).
2b) Effect of level and solubility of CP on milk and
milk protein production.
Ouring early lactation, milk production may increase as
much as 10 to 20% when dietary CP level is raised from about

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17
13 to 15% to 16 to 19% (Satter and Roffler, 1975). However,
in order to minimize N losses in the rumen, diets with high
levels of CP must include significant amounts of rumen
escape proteine
Several studies have shown that increasing the supply
of undegraded dietary CP to early lactating cows stimulates
milk production. Milk production was increased with
postruminal infusion of case in and other proteins (Clark,
1975; Clark et al, 1977; Spires et al, 1975; ~rskov et al,
1977). Shingoethe et al (1988) found that cows fed heated
SBM produced more milk than those fed unheated SBM;
methionine supplementation to SBM diets also caused milk
yield to increase (Shingoethe et al, 1988).
Madjoub et al (1978) found that cows produced more milk
with high protein (HP), low solubility (LS) diets than with
LP-LS diets; LP-LS diets in turn helped produce more milk
than HP-HS or LP-HS diets. However, Robinson and Kennelly
(1988) found that late-Iactating cows did not respond to
increased supply of undegraded dietary proteine
Rumen escape proteins do not appear to have an effect
on milk prote in concentration (Madjoub et al, 1978; Robinson
and Kennelly, 1988); Emery (1978) suggested that dietary
protein affects total milk protein more than it affects
concentration of protein in milk. Emery (1978) found a
slight increase in milk protein percentage due to dietary
CP: .02% for each increase of dietary CP of 1%. Schingoethe
(1988) found that milk prote in percentages were highest with

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18
HS than with 15 diets; however, in cases where milk yield
was increased, actual milk protein yield may increase.
Postruminally infused proteins on the other hand tend to
increase milk protein concentration and yield (Spires et al,
1975; Clark et al, 1977).
Greater response with abomasal
infusions than with dietary manipulations suggest that
specifie amine acids may limit concentration of protein in
milk (Emery, 1978).
Other factors affect milk protein concentration; There
appears to be a negative relationship between level of
dietary fiber and milk protein concentration; whereas intake
of dietary energy appears to have a positive effect on milk
prote in concentration (Emery, 1978). Consequently, there
seems to be an inverse relationship between milk fat and
milk proteine
3) Low Milk protein and the Relationship Between Dietary
Fat, Metabolism in the Rumen and Milk Protein Synthesis.
Several studies have shown that milk protein
concentration or yield may decrease with the addition of fat
(Anderson et al, 1979; Banks et al, 1976; Bines et al, 1978;
Dunkley et al, 1977; MacLeod et al, 1977; Sharma et al,
1978; Palmquist and Moser, 1981; Henderson et al, 1985).
Milk protein has also increased with protected soybean oil
or remained unchanged with hydrogenated soybean oil (Astrup
et al, 1976), protected sunflower seed (Earle et al, 1976)
and protected oils (Goering et al, 1976;1977). Based on such

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19
results, smith et al (1978) have suggested that the response
of milk protein may be related to degree of saturation of
the protected lipide
Dunkley et al (1977) found that dietary fat
specifically affected the case in fraction of milk proteine
There appears to be an interaction between dietary fat and
protein metabolism in lactating dairy cows that generally
results in lowered milk protein yield. However, it is not
known whether this occurs intraruminally, postruminally or
during the post absorptive stage.
Polymerized unsaturated long chain carboxylic acids
have been used to increase the amount of prote in escaping
ruminaI degradation (Chalupa, 1975). Proteins have been
coated with 15% fat to increase REP yield. However, fat
level normally does not exceed 4 to 10% in production diets.
Palmquist and Conrad (1978) have found that although N
digestibility may increase with the addition of fat, N
retention is not affected.
Several hypotheses have been proposed to explain this
phenomenon, including: a) decreased supply of microbial
protein; b) decreased availability of glucose; c) decreased
plasma insulin level or decreased sensitivity of tissues to
insulin; and d) direct effect of LCFA causing a decrease in
the synthesis of milk proteins.
a) Decreased supply of microbial crude protein (MCP):
When starch energy is replaced by energy from fat,

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20
significant amounts of energy are not available for
fermentation and microbial growth (Smith et al 1978).
Decreased HCP synthesis has been reported by Dunkley et al
(1977) in cows receiving fat. Unprotected tallow fatty acids
have increased the efficiency of HCP synthesis by 39% over
control diets and by 67% over diets containing calcium soaps
(Jenkins and palmquist, 1984). This increase in efficiency
is attributed at least in part to an inhibition of the
growth and metabolism of protozoa; calcium soaps presumably
do not inhibit protozoa. It is difficult to conclude from
that study because flow of HCP to the duodenum was higher
for the control due to higher N intake by cows fed the
control diet. In a study with beef steers, Boggs et al
(1987) found that unprotected tallow increased efficiency of
HCP synthesis; however, total HCP reaching the abomasum was
low due to lower digestion coefficients for organic matter
in tallow diets.
It would appear therefore that although efficiency of
HCP synthesis may increase, total HCP available from the
rumen is often lower than in control diets. This would mean
that the protein level in fat diets needs to be higher than
in conventional diets; This may be achieved by increasing
total CP percentage or more efficiently by substituting part
of the dietary protein with less degradable proteins.
b) Decreased availability of glucose: Hilk yield and
milk energy output have often increased with the addition of

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21
fat in dairy cow diets (Smith et al, 1978). Glucose provides
carbon atoms for the synthesis of lactose and energy for MCP
synthesis and it is thought there may be a limited supply
when dietary fat is fed. Dietary fat has decreased plasma
glucose in some studies (Palmquist and Moser, 1981), but
others found there was no effect of fat on plasma glucose
level (Palmquist and Conrad, 1978). Nevertheless, it is
believed that a depression in blood glucose would cause a
depression in rate of lactose synthesis which, in turn,
would cause a reduction in the amount of fluid volume (Rook
et al, 1965). A decrease in glucose availability could limit
protein synthesis by limiting synthesis of non essential
amino acids. Since milk yield often increases with the
addition of fat, it follows that glucose availability is
probably not limited. Furthermore, the decrease in ruminaI
acetate: propionate ratio often associated with dietary fat
may be due to increased propionate production; since
propionate is a glucose precursor, increases in glucose
supply should parallel decreases in acetate: propionate
ratio observed with fat feeding. Thus, a deficiency in
glucose is not supported by current data.
c) Decreased plasma insulin level or decreased tissue
sensitivity of tissues to insulin (Palmquist and Moser,
1981). Insulin has been shown to stimulate lactose and lipid
synthesis (Martin and Baldwin, 1971) in isolated rat mammary
cells in vitro; Martin and Baldwin (1971) found that casein
synthesis was slightly stimulated by insulin. Insulin is

---

22
known to stimulate the transport of neutral amine acids in
isolated rat hepatocytes (Kilberg, 1982). Studies in the
bovine indicate that while short-acting insulin injections
into lactating cows increase milk protein concentration,
they also decrease milk yield (Schmidt, 1967; Rook et al,
1965), and milk protein yield is unchanged. It is therefore
not clear whether the increased milk prote in content is due
to increased protein synthesis or to decreased fluid volume.
Lavau et al (1979) suggested that due to inhibition of
acetyl-CoA carboxylase activity, NADPH utilization decreases
and oxidation of glucose through the pentose phosphate
pathway decreases, causing glucose uptake to decrease. Fat
diets have increased insulin resistance in one experiment
and decreased plasma insulin level in another (palmquist and
Moser 1981). Palmquist and Moser (1981) concluded that such
events would affect utilization of amine acids for milk
protein synthesis if insulin stimulates amine acid transport
in mammary tissue. Decreased tissue sensitivity to insulin
would infer that insulin would bind less readily to mammary
cell; however, this is somewhat contradicted by findings of
smith et al (1987) that dietary fat increases insulin
binding to milk fat globules.
d) direct effect of LCFA causing a decrease in the
synthesis of milk proteins. It has been suggested that
dietary fat May decrease glucose metabolism in mammary and
adipose tissue of lactating cows (Smith et al, 1978). Yang

---

23
et al (1960) have shown that dietary fat causes FA synthesis
and glucose oxidation to decrease in adipose tissue of cows
fed high fat diets. Cummins and Russell (1985) found that
feeding whole cottonseed to lactating cows decreased glucose
and palmitate uptake and decreased glucose oxidation in
adipose and mammary tissue. Therefore, the possibility
exists that LCFA may also inhibit synthetic processes
leading to the production of milk proteine
e) Other possible explanations:
Decreased availability of acetate. Prote in synthesis
and the active transport of precursors into mammary cells
require not only EAA but also energy in the form of ATP. In
the mammary gland, glucose is essentially used for lactose
synthesisi some glucose is also used for the synthesis of
glycerol and NEAA. Most of the ATP produced in the gland is
derived from the oxidation of acetate, with a small
contribution of beta-hydroxybutyrate and amine acids (Davis
and Mepham, 1976).
As discussed previously, fat depresses fiber digestion
in the rumen and limits the supply of acetatei dietary fat
may indirectly inhibit the synthesis of prote in and lactose
by limiting the supply of a preferential energy source to
the mammary gland. One immediate consequence of such a
theory is that if aIl other substrates are available, post-
ruminaI infusion of acetate should increase milk protein
synthesis. Indeed, when the VFA's were infused into the
abomasum of lactating cows, only propionate and acetate

---

24
increased milk yield (Rook and Balch, 1961). However, while
propionate also increased milk protein concentration,
acetate increased lactose production and increased fluid
yield, and failed to increase the concentration of milk
proteine
The fact that propionate stimulates milk protein
synthesis can not be attributed to an increased glucose
supply since postruminal glucose infusion does not increase
milk protein content or yield (Clark et al, 1977). It can
not be attributed to increased insulin secretion, since
glucose, like propionate elicits insulin secretion in vivo,
and would therefore have the same effect as propionate on
milk proteine Furthermore as discussed previously, decreased
plasma insulin occurs in cows fed fat. It must be that
propionate is an energy source secondary to acetate, and
that the mammary gland is capable of utilizing both acetate
and propionate.
One other problem with this view relates to the
inability of protected fats to increase milk protein
synthesis. However, the postulated effect of acetate relates
to milk prote in yield, not milk protein concentration.
Current data shows that in most instances where protected
fats were fed, milk protein concentration may decrease (due
to increased milk volume), but milk protein yield is
unaffected (DePeters et al, 1987; Rindsig and Schultz, 1974;
Dunkley et al, 1977; Palmquist and Conrad; 1978; palmquist
and Moser, 1981; storry et al, 1974a). Where enough

---

25
unprotected fat was fed to lower fiber digestion and
decrease acetate production in the rumen, milk protein yield
was decreased (Storry et al, 1974a): Where protected fat did
not affect fiber digestion or acetate production, milk
protein yield was unaffected (storry et al, 1974a). Emery
(1978) has demonstrated the existence of a negative
relationship between intake of fiber and milk protein
concentration. But again this relates to concentration, not
yield.
It is, however, difficult to conceive that acetate
alone would play that much of a role in milk protein
production, otherwise high concentrate-Iow roughage diets
would also limit synthesis of milk protein.
Low protein: calorie ratio in fat-containing diets.
This theory relates to the ability of dairy cows to mobilize
body tissues for milk production. Cows in early lactation
depend on body tissues for part of their nutrient
requirements. One kg of body fat supplies energy to produce
approximately 7 kg of milk (Schmidt et al, 1988), and
supplies some amount of protein: tissue fat is mobilized
more readily and in larger quantities than tissue proteins.
Since adipose tissue mobilization is inhibited by
dietary fat, the supply of protein from tissues may be
reduced as weIl. Furthermore dietary fat sources such as
tallow and vegetable oils often replace corn and other
starch materials: this causes the protein to calorie ratio
of the ration to decline. If this theory holds, correcting

---

26
the protein-to-calorie ratio in fat-containing diets may
help to restore normal milk protein content.
Dietary fat may contribute to milk production,
particularly in early lactating and high producing cows.
However, feeding fat appears to interact with prote in
metabolism in dairy cattle. This causes protein nutrition of
cows fed fat to gain renewed importance. Further evidence is
needed to assess the true role of energy and protein supply,
precursors, body tissues and metabolic hormones such as
insulin in protein synthesis by the mammary gland.

---

27
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Inc., Englewood Cliffs. p. 66.
80.
Sharma, H.R., J. Ingalls, J.A. McKirdy. 1978.
Replacing barley with protected tallow in the ration
of lactating Holstein cows. J. Dairy Sei. 61:574.
81.
Smith, D.H., K.L. Roehrig, D.L. Palmquist and F.L.
Schanbacher.1987. Effects of dietary fat and lactation
status on insulin binding to bovine milk fat globule
membranes. J. Dairy Sei. 70:1557.

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38
82.
Smith, N. E., W.L. Dunkley, and A.A. Franke.1978.
Effects of feeding protected tallow to dairy cows in
early
lactation. J. Dairy Sei. 61:747.
83.
Spires, H.R., J.H. Clark, R.G. Derrig and C.L. Davis.
1975. Milk production response and Nitrogen
utilization in response to postruminal infusion of
sodium caseinate in Lactating cows. J. Nutr. 105:1111.
84.
Spires, H.R., J.H. Clark, R.G. Derrig and C.L. Davis.
1975. Milk production response and Nitrogen
utilization in response to postruminal infusion of
sodium caseinate in
Lactating cows. J. Nutr.
105:1111.
85.
Spires, H.R.,J.H. Clark, R.G. Derrig, and C.L. Davis.
1975. Milk production and nitrogen utilization in
response to
postruminal infusion of sodium caseinate
in lactating
cows. J. Nutr. 105:1111.
86.
Steele, W. and J.H. Moore. 1968. The digestibility
coefficients of myristic, palmitic and stearic acids
in the diets of sheep. J. Dairy Res. 35:371.
87.
Steele, W., Noble, R.C. and J. H. Moore. 1971. The
effects of two methods of incorporating soybean oil
into the diet on milk yield and composition in the
cow. J. Dairy Res. 38:43.
88.
Storry, J.E., P.E. Brumby, A.J. Hall, and B. Tuckley.
1974b. Effects of free and protected forms of codliver
oil on milk on milk fat secretion in the dairy cow.
J. Dairy
Sei. 57:1046.

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39
89.
Storry, J.E., P.E. Brumby, A.J. Hall, and V.W.
Johnson. 1974a. Response of the lactating cow to
different methods of incorporating casein and coconut
oil in the diet. J. Dairy
Sci 57:61.
90.
Swift, R.W., E.J. Thatcher, A. Black, J.W. Bratzler,
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91.
Van Soest, P.J. 1963. Ruminant fat metabolism with
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92.
Vance, D.E. 1983. Metabolism of fatty acids and
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In: G. Zubay Ced.)
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93.
White, T.W., R.B. Grainger, F.H. Baker, and J.W.
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47:1978.

---

INFLUENCE OF LEVEL OF DIETARY FAT AND PROTEIN
ON MILK PRODUCTION, MILK COMPOSITION AND
RATION DIGESTIBILITyl
1 A. J. Nianogo and H. E. Amos. Ta be submitted ta
Nutrition Reports International.
40

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41
ABSTRACT
sixteen multiparous (M) and eight primiparous (P)
Holstein cows 30 to 60 days in lactation were blocked into 4
balanced groups of 6 cows based on milk yield for a 56-day
study. The groups were randomly assigned to 1 of 4 dietary
treatments to determine the effect of protein level in diets
containing added lipids on intake, digestion, milk yield,
milk composition and body weight changes.
Treatments were:
A) control plus .45 kg corn/d; B) control .45 kb soybean
meal (SBM)/d; C) control + .45 kg corn/d + 4% fat; 0)
control + .45 kg/day SBM plus 4% fat.
Sorghum (Sorghum
bicolor L.) silage provided the roughage. Dry matter intake
(DMI) was not affected by fat or protein addition. However,
DMI was higher for M than for P cows and silage intake was
lower for cows receiving fat. Cows fed 4% fat produced more
milk and tended to produce more milk fat than cows fed diets
without fat. Cows fed 0 gained more weight than cows fed B
or C. Dietary fat increased crude prote in and gross energy
digestibility. In this study fat did not alter DMI or milk
CP concentration. Feeding dietary fat and supplemental
protein together contributed to higher weight gains while
maintaining adequate level of production.
KEY WORDS: dietary fat, protein level, protein: calorie
ratio, age, milk yield, milk composition.
INTRODUCTION
The addition of lipids to diets for lactating dairy cows has
often increased milk production (1) and milk fat yield (2,

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42
3, 4) in animaIs with a negative energy balance. However,
rumen unprotected dietary fat also has some negative
effects, including decreased fiber digestibility (5),
decreased dry matter intake (4) and decreased milk protein
percentage (2, 3, 4, 6) or yield (2, 4). Decreased dry
matter intake (DMI) May offset the objective of increased
energy intake with the addition of dietary fat and May
accentuate a negative N balance. Decreased milk protein is a
concern because of the importance of casein in cheese
production.
While increasing energy density, dietary fat alters
the normal protein: calorie ratio. Furthermore, Palmquist
and Conrad (1) observed a slight increase in yield of milk
and milk protein when cows receiving a protected fat
supplement were fed additional CP. Perhaps there would be
some benefit in maintaining the protein to calorie ratio by
increasing the protein allotment for cows receiving
significant amounts of fat.
The objectives of this study were to determine the
effects of increasing protein intake (maintaining a constant
protein to calorie ratio) in cows receiving diets containing
added lipids upon milk production, milk composition and
ration digestibility.
MATERIALS AND METHODS
Sixteen multiparous (M) and eight primiparous (P) Holstein
cows 30-60 days in lactation were blocked into 4 balanced

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43
groups of 6 cows based on milk yield. The groups were
randomly assigned to 1 of 4 dietary treatments arranged in a
2x2 factorial design with 2 P and 4 M cows per treatment.
The experiment was designed for 2 weeks of adjustment
followed by two 28-day experimental periods. Sorghum silage
and 2 basal concentrates containing no added fat (control,
CL) or 6.82% added fat (test concentrate, TC) provided the
bulk of the diet, which was then supplemented with .45
kg/day of either corn (Zea mays L.) or SBM.
Lipid source
was yellow grease.
Dietary treatments were arranged as follows: A) CL
(balanced to meet NRC recommendations for protein and
energy) plus .45 kg ground corn/day (d); B) C plus .45 kg
SBM/d; C TC (same as A but with fat providing approximately
4% of the total dry matter intake) plus .45 kg corn/d; D) TC
plus .45 kg SBM/d.
Basal diets contained ground shelled
corn, corn gluten.feed, soy hulls and SBM (table 1) and were
fed using a BOUMATIC2 computerized feeder with two feeding
stations; ground corn and SBM supplements were top-dressed
on the silage and fed through CALAN3 gates.
Sodium
bicarbonate and a trace mineraI mix were provided ad
libitum.
Cows were trained to use feeders and CALAN gates
for about one wk, and fed diet A plus sorghum silage ad
libitum for 2 additional wk to provide data for covariate
analyses of experimental data. Milk yield was recorded daily
and milk samples were collected during the last wk of

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44
adjustment for determining baseline milk yield and
composition.
Cows were offered silage at 110% of expected daily
intake. DMI and milk yield were monitored daily; cow weights
were determined on 3 consecutive d biweekly. Milk was
sampled (aliquot of 20 ml at a.m. and p.m. milking) for 7
consecutive d) during wk 4 and 8, preserved with 1 ml of 10%
formaldehyde and stored at 40 C until analyzed. Fecal grab
samples were collected at 0800 (d 1), 1000 (d 2), 1200 (d
3), 1400 (d 4), 1600 (d 5), and 1800 (d 6) hour during wk 4
and 8; fecal samples were dried at 60 0 C for 72 h, ground and
composited.
Diets, orts and fecal samples were oven dried
at 60° C for 72 h to determine dry matter, and ground
through a 1 mm Wiley mill screen. These samples were
analyzed for gross energy and ash according to AOAC (7) and
for neutral detergent fiber, acid detergent fiber,
cellulose, hemicellulose and lignin according to procedures
described by Robertson and Van Soest (8). Total milk solids
were determined in duplicate on 10 ml of milk lyophilized in
Gooch crucibles on a Labconco Model 75040 lyophilizer4 . Milk
fat was determined by Babcock (7). AlI crude protein
determinations were performed on a Technicon Model II
autoanalyzer5 after digestion on a block digester.
Digestibility data was obtained using ash-free
indigestible ADF (IADF) as a marker. The IADF content was
determined by incubating samples of silage, protein
supplements, concentrates, orts and feces with one volume of

---

45
rumen fluid and two volumes of McDougall's buffer in vitro
for 120 h as described by Tilley and Terry (9); in vitro
sample residue and media were then filtered through ADF
crucibles and residue was submitted to an ADF digestion
(10). Apparent digestibility coefficients (ADC) were
calculated as follows: ADCDM = 100 x 1.00-(IADFd/IADFf);
where IADFd and IADFf are the concentration of IADF in diet
and feces, respectively. Total fecal DM was quantitated as:
fecal DM (kg) = DMI (kg) - DMI (kg)xADC (kg). ADC for CP, GE
and fiber components were determined based on concentration
in diet versus concentration in feces.
AlI data were analyzed separately for each of the two
experimental periods; where no difference due to period was
determined, data were pooled for further analyses.
Statistical analysis of the data was performed using SAS
general linear model procedures (11). Main effects were
level of fat (CL vs. TC), prote in treatment (corn vs. SBM)
and age (M vs P). Diets (A, B, C and D) were also compared
to determine the effect of level of fat by prote in treatment
combination.
RESULTS AND DISCUSSION
Ingredient composition of the concentrates and
nutrient composition of aIl dietary components are shown in
table 1. AlI results are pooled data from the two 28 d
periods unless indicated otherwise. As expected, the calorie
density was greater for the concentrate containing fat. The

---

46
prote in to calorie ratio was .11 kg/Meal for both
concentrates. Main effect influence on nutrient intakes are
in table 2. Dry matter intake was not influenced by fat or
prote in addition. Cows fed 4% fat consumed more (P<.Ol) NEL
(calculated using NEL values (12», less ADF (P<.05) and
more CP (P<.05) during the first 28 d period (3.49 vs. 3.27
kg/day). Neutral detergent fiber intake tended to increase
but CP intake was only slightly increased by the addition of
.45 kg 5MB/day. Cows receiving CL consumed more (P<.05)
silage, increasing NEL intake by 1.08 Mcal/d. Multiparous
cows consumed higher (P<.OOOl) amounts of DM, CP, NDF, ADF
and NEL than P cows throughout the study.
Milk yield data are in table 3.
Cows receiving 4% fat
produced 4.3% more milk (P<.06) than those fed CL. Adjusted
least square means (LSM) for milk yield were similar for P
and M cows. Milk fat yield was slightly increased by the
addition of fat and M cows tended to produce more (P<.07)
fat than P cows. Milk prote in percentage and yield was not
affected by the addition of fat. This agrees with results
from storry et al (4), Earle et al (13) and Goering et al
(10 and 14) but conflicts with other results (2, 3, 4 and
6) •
In this study, additional prote in provided in the form
of .45 kg/day SBM replacing .45 kg/day corn maintained the
prote in to calorie ratio of cows fed 4% fat equal to those
fed the control concentrate.
Efficiency of milk protein
production (kg milk CP/kg CP consumed) was slightly (P<.07)

---

47
depressed in cows receiving concentrates containing added
fat. Additionally, cows fed fat did not respond to increased
prote in intake, thus contributing to the lower protein
ration (C) yielding more (P<.007) milk protein per unit
prote in consumed.
Some of the supplementary protein May have been
directed to body weight gain since live weight gain tended
to increase with higher dietary prote in (table 2). Cows fed
diets A, B, C, and D consumed 8.91, 9.46, 8.69, and 8.83 kg
of NDF daily, corresponding to 44.98, 48.29, 45.12 and
45.82% of daily DMI, respectively. Mertens (15) found that
maximum daily DMI and solids-corrected milk resulted when
the ration contained 39.1 + 1.8%
and 37.8 ± 2.9% NDF,
respectively. However, cows with controlled concentrate
intake and silage ad libitum May have a higher NDF intake,
depending on amount of concentrate consumed. Dietary NDF
content has been suggested as being the factor which yields
the greatest correlation with DM intake (15).
Cows fed D consumed the highest amount of NEL and the
lowest amount of silage (table 4), had the highest digestion
coefficients for DM, CP and GE (table 7) and gained more
weight than cows fed B or C.
Since intake of DM was not
affected by diet, the lower silage consumption by cows fed
diet C indicates that these cows consumed more concentrate
than other groups.
Apparent digestibility coefficients are listed in
tables 5 (main effects) and 7 (effect of treatment

---

48
combinations). Dry matter digestibility tended to be greater
for fat fed cows. Dietary fat also resulted in higher CP
(P<.OOl) and gross energy (P<.04) digestibility
coefficients. Increased protein digestibility has been
previously reported by Palmquist and Conrad (1). However,
protein digestibility has not increased in other studies (6
and 16). Nutrient digestibility was generally not affected
by level of dietary prote in or by age. On the effect of fat
by protein treatment combination, diet 0 produced higher
digestion coefficients for dry matter (68.46), CP (69.69)
and energy (68.14) than diet B (65.07, 61.38 and 63.72).
Digestibility of fiber components was not affected.
It is possible that under situations where dietary fat
is fed, physiological conditions are such that the protein
to calorie ratio is below normal, requiring more protein
than the amount fed in this study. Although protein
digestibility may increase in fat-fed cows, N retention
remains unchanged (5). A higher level of dietary CP or a
greater level of rumen escape prote in may prove useful.
In fa ct ~rskov et al (17) have obtained significant
increases in milk, milk fat and milk protein with abomasal
infusions of case in in Friesan cows in early lactation and
negative energy balance. Under our conditions there appears
to be no benefit in protein supplementation in cows
receiving dietary fat from the standpoint of milk prote in
production. However, cows fed higher levels of both energy
and prote in (diet 0) gained significantly more weight than

---

49
those on a lower energy or protein diet, which may be
important for subsequent lactations.

---

50
REFERENCES
1.
palmquist, D.L., and Conrad, H.R. 1978. High fat
rations for dairy cows. Effects on feed intake, milk
and fat production, and plasma metabolites. J. Dairy
Sei. 61:890.
2.
Dunkley, W.L., Smith, N.E., and Franke, A.A. 1977.
Effects of feeding protected tallow on composition of
milk and milk fat. J. Dairy Sei. 60:1863.
3.
Palmquist, D.L. and Moser, E.A. 1981. Dietary fat
effects on blood insulin, glucose utilization, and
milk prote in content of lactating cows. J. Dairy Sei.
64:1664.
4.
Storry, J.E., Brumby, P.E., Hall, A.J., and Johnson,
V.W. 1974. Response of the lactating cow to different
methods of incorporating casei~ and coconut oil in the
diet. J. Dairy Sei. 57:61.
5.
Palmquist, D.L., and Jenkins, T.C. 1980. Fats in
lactation: Review. J. Dairy Sei 63:1.
6.
DePeters, E.J., Taylor, S.J., Finley, C.M., and
Famula, T.R. 1987. Dietary fat and nitrogen
composition of milk from lactating cows. J. Dairy Sei
70:1192.
7.
AOAC. 1984. Official Methods of Analysis (14 th ed.).
Assoc. Offic. Anal. Chem. Washington, D.C.
8.
SAS. 1982. SAS user's guide. Statistical Analysis
system Institute, Inc. Cary, N.C.

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51
9.
Tilley, J. M. A., and Terry, R.A. 1963. A two-stage
technique for the in vitro digestion of forage crops.
J. Brit. Grassl. Soc. 18:104.
10.
Goering, H. K., Gordon, C.H., Wrenn, T.R., Bitman, J.,
King, R.L., and Douglas, F.W., Jr. 1976. Effect of
feeding protected safflower oil on yield, composition,
flavor, and oxidative stability of milk. J. Dairy Sei.
59:416.
11.
Robertson, J.B., and Van Soest, P.J. 1981. The
detergent system of analysis and its application to
human foods. p. 123 In: W. P. T. James and o. Theander
(ed.) The Analysis of dietary fiber.
Marcell Dekker,
New York, NY.
12.
National Research Council. 1978. Nutrient
Requirements of Dairy Cattle. 5th revised ed. Natl.
Acad. Sei., Washington, D.C.
13.
Earle, D. F., Pankhurst, I.M., Mathews, G.L., Fowler,
P., and Robinson, I.B. 1976. Responses in linoleic
acid content of milk fat from cows receiving different
levels of protected sunflower seed supplement.
Australian J. Dairy
Tech. 31:48.
14.
Goering, H. K., Wrenn, T.R., Edmondson, L.F., Weyant,
J.R., Wood, D.L., and Bitman, J. 1977. Feeding
polyunsaturated vegetable oils to lactating dairy
cows. J. Dairy Sei. 60:739.
15.
Mertens, D.R. 1985. Factors influencing feed intake in
lactating cows: from theory to application using

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52
neutral detergent fiber.
P. 1-18.
Proc. Ga. Nutr.
Conf.
for the Feed Industry.
Atlanta, GA.
16.
Palmquist, D.L., and Conrad, H.R. 1980. High fat
rations for dairy cows. Tallow and hydrolyzed blended
fat at two intakes. J. Dairy Sei. 63:391.
17.
~rskov, E. R., Grubb, D.A., and Kay, R.N.B. 1977.
Effect of postruminal glucose or prote in
supplementation on milk yield and composition in
Friesian cows in early lactation and negative energy
balance. Br. J. Nutr. 38:397.

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53
FOOTNOTES
1Boumatic Dairy Equipment Co. A division of D.E.C., Inc.
2American Calan, Inc. P. O. Box 307, Jenness Pond Rd.
Northwood, NH 03261.
3Labconco Freeze Dryer Model 75040. Kansas City, MO.
4Specifications for the Technicon Autoanalyzer II
continuous-flow Analytical Instrument (Technical
Publication No. TSO-0170-2). 1975. Technicon
Instruments Corp. Tarrytown, NY

---

Table 1. Percentage ingredient compositiona and partial
compositional analyses of diets fed lactating dairy cowsa .
pIETARY COMPQNENT
Item
CLb
TCb
silage
SBM
Corn
Ingredient (t):
Corn gluten feed
18.94
18.54
Soy hulls
18.94
18.54
Ground corn
42.42
34.71
---
---
100.00
Soybean meal
18.28
20.28
---
100.00
Dical
1.14
.74
Limestone
.38
.37
Fat
---
6.82
Silage
---
---
100.00
Nutrient content (t)
Dry matter
91. 63
92.13
20.00
90.63
90.35
Crude protein
21.17
22.77
9.28
51.13
8.72
NDF
28.51
26.54
72.91
14.30
12.29
ADF
11. 56
11.72
43.22
5.57
2.69
Lignin
1.01
.45
6.61
.40
.35
Ether extract
4.50
10.30
3.30
---
4.50
Energy (Mcal/kg)
3.81
4.23
4.04
4.69
4.55
NEL (Mcal/kg)c
1.90
2.10
1. 32
1.86
2.03
Ash
5.64
5.32
7.35
7.77
1. 52
protein:NELd
.11
.11
.07
.27
.04
aDry matter basis.
bCL: control; TC: test concentrate.
cCalculated from NRC,
1978.
U1
...
dkg crude protein in l
kg DM/Mcal NEL in 1 kg DM.

---

Table 2. Nutrient intake and body weight of lactating cows as
affected by level of fat, protein supplement or age.
Level of fat
Supplement
Age
Pooled
Item
0
4%
Corn
SBM
P
M
S.E.
---------------------(kg)----------------------
DMI
19.70
19.27
19.53
19.43
17.65c
21.32 d
.41
Silage
7.84 a
7.02 b
7.49
7.47
7.04 e
7.82 f
.21
CP
3.23
3.26
3.17
3.32
2.91 c
3.58d
.08
NDF
9.18
8.76
8.80
9.14
8.25c
9.69 d
.18
ADF
4.80a
4.49b
4.67
4.62
4.29 c
5.00d
.10
Hemicel. g
4.18
4.01
4.11
4.08
3.75
4.44 d
.08
Cellulose
4.17
4.96
4.09
4.05
3.75c
4.39 d
.08
Body weight 578
577
570
585
550e
605 f
10.02
Weight gain
3.94
7.06
3.69
7.31
8.50
2.50
3.05
---------------------(Mcal)--------------------
NEL
30.06c
32.30d
31.25
31.11
28.14 c
34.22 d
.72
----------------------(%)----------------------
DMI/BWh
3.42
3.37.
3.43
3.36
3.26a
3.53b
.06
abcdefFor each main effect, means in the same row with no common
superscript are different at
P<.05 (a,b), P<.Ol (c, d), P<.06
(e,f).
gHemicellulose.
h 1 00 x DMI (kg) /
Body Weight (kg).
U1
U1

---

Table 3. Yield and composition of milk from lactating cows as
affected by level of fat, protein supplement or age.
Level of fat
Supplement
Aqe
Pooled
Item
o
4%
Corn
SBM
pa
Ma
S.E.
--------------------(%)----------------------
Total solids 12.35
12.05
12.25
12.14
12.11
12.28
.15
Fat
3.11
3.14
3.06
3.19
3.08
3.17
.05
SNF
9.22
8.90
9.15
8.97
8.99
9.13
.13
CP
3.29
3.29
3.32
3.25
3.28
3.30
.06
MineraIs
.74
.72
.73
.74
.73
.73
.01
Lactose
5.17
4.87
5.10
4.94
4.91
5.14
.11
------------------(kg/day)-------------------
Milk
27.78b 28.90
28.54
28.15
28.73
27.95
.67
Fat
.79d
.88 e
.84
.84
.76 f
.91g
.02
SNF
2.43
2.49
2.50
2.41
2.38
2.53
.06
CP
.88
.91
.93
.87
.88
.91
.03
LactQse
1.31
1.37
1.37
1.31
1.23
1.45,
.04
MPPIJ
.30 f
.27g
.32h
.25 i
.31h
.26 1
.01
ap: primiparous COWSi M: multiparous cows.
bcdefghi For each main effect, means in the same row with no common
superscript are diffe+ent at P<.06 (b, cl, P<.04 (d, el,
P<.07 (f, g), P<.OOl (h, 1).
jkg Milk protein per kg CP intake.
U1
en

---

Table 4. Nutrient intake and body weight of lactating dairy cows as
affected by treatment combination.
Dieta
Item
A B C
0
S.E.
--------------------(kg)--------------------
DMI
19.81
19.59
19.26
19.27
.41
silagee
7.41bc
8.27 c
7.38bc
6.66 b
.21
CP
3.20bc
3.26bc
3.13b
3.39c
.08
NDF
8.91bc
9.46b
8.69c
8.83 bc
.18
ADF
4.74bc
4.86b
4.60bc
4.38 c
.10
Hemicellulose
4.17
4.19
4.06
3.96
.08
Cellulose
4.13 bc
4.22 b
4.05bc
3.88c
.08
Body weight
573
582
567
588
10.02
Weight gain
9.88bc
-2.0b
-2.50b
16.63c
3.05
-------------------(Mcal)-------------------
NEL
30.40bc
29.72b
32.11cd
32.50d
.72
---------------------(%)--------------------
DMI/BW
3.71
3.52
3.56
3.55
.06
aA: control + corn: B: control + SBM: C: fat + corn: 0: fat + SBM.
bcdMeans with in the same row with no common superscript are
different at P<.Ol (silage), P<.05 (CP, cellulose, NDF,
ADF, weight gain). For NEL' A is different from C (P<.06)
and 0 is different from B (P<.04) and from C (P<.02).
eFat* Protein interaction (P<.05).
Ut
"

---

Table 5. Nutrient digestibility (%) by lactating dairy cows as
affected by level of fat,
level of protein supplement or
age.
Leyel of fat
Supplement
Age
Pooled
Item
0
4%
Corn
SBM
pa
Ma
S.E.
Dry matter
65.70
67.46
66.39
66.77
65.89
67.26
.52
CP
61. 77 b 68.16c
64.39
65.53
63.80
66.12
.97
Gross energy 64.59 d 67.12 e
65.78
65.93
65.24
66.47
.58
NDF
53.51
53.16
53.38
53.29
52.73
53.95
.45
ADF
53.51
52.89
53.52
52.68
52.87
53.34
.44
Hemicel. f
53.64
52.74
52.82
53.56
52.16
54.22
.58
Cellulose
63.25
62.78
62.90
63.14
63.43
62.61
.44
ap: primiparous cows; M: multiparous cows.
bcdeFor each main effect, means in the same row with no
common superscript are different at P<.OOl (b, c) or
P< • 04
(d, e).
fHemicellulose.
U1
co
"

---

Table 6. Yield and composition of milk from lactating dairy
cows as affected by treatment combination.
Dieta
Item
A B C
0
S.E.
-------------------(%)--------------------
Total solids
12.49
12.20
12.01
12.09
.15
Fat
3.07
3.14
3.15
3.24
.05
SNF
9.56
9.07
8.94
8.86
.13
CP
3.32
3.26
3.33
3.24
.06
MineraIs
.74
.75
.72
.72
.01
Lactose
5.34
5.00
4.87
4.88
.11
-----------------(kgjday)-----------------
Milk
27.88
27.69
29.20
28.61
.67
Fat
.79
.800
.88
.88
.02
SNF
2.44
2.39
2.66
2.43
.06
CP
.91
.85
1.55
.88
.03
Lactose
1.33
1.29
1.42
1.32
.04
MPPIe
.33 bc
.26
.30c
.24d
.01
aA: control + corn; B: control + SBM; C: fat + corn; 0: fat + SBM.
bcdMeans in the same row with no common superscript are
different; diet A is different from 0 (P<.002) and C
(P<.0002), and B is different from C (P<.007) and from 0
(P<.06).
ekg Milk protein per kg CP intake.
01
\\0

---

Table 7. Nutrient digestibility (%) of diets fed lactating dairy
cows as affected by treatment combination.
Dieta
Item
A
B
C
0
S.E.
Dry matter
66.34 bc
65.07 c
66.45bc
68.46b
.52
CP
62.16cd
61. 38c
66.62 cd
69.69 b
.97
Gross energy
65.46bc
63.72 c
66.10bc
68.14 b
.58
NDF
53.76
53.26
53.00
53.32
.45
ADF
54.16
52.45
52.87
52.90
.44
Hemicellulose
53.24
54.04
52.39
53.08
.58
Cellulose
62.57
63.94
63.23
62.33
.44
aA: control + corn; B: control + SBM; C: fat + corn; 0: fat + SBM.
bcdMeans in the same row with no common superscript are
different at P<.04
(DM) or P<.Ol (Gross energy). For CP,
diet A is different from C (P<.004), and 0 is different
from B (P<.03) and from C (P<.002).
O'l
o

---

INFLUENCE OF TOASTED SOYBEAN MEAL IN DIETS CONTAINING ADDED
LIPIDS ON MILK YIELD, MILK COMPOSITION AND EFFICIENCY OF
PRODUCTION1.
1Nianogo, A. J. and H. E. Amos. To be submitted to
Journal of Dairy Science.
61

---

62
ABSTRACT
Twelve Holstein cows in mid lactation were blocked in
two groups of 6 according to production and days in milk to
determine the effect of dietary fat and prote in level and
solubility on milk yield and composition.
Cows were
randomly assigned to one of two 3x3 Latin Squares; cows in
one square were fed a control concentrate with no added fat
(C) while cows in the other square received a concentrate
with 9.3% fat (F). Squares included three 21-d. periods,
three sub-blocks of 2 cows each and three protein
supplements: 2.3 kg/do of either a) solvent extracted
soybean meal (SBM), b) toasted SBM (TSBM) or c) low protein
(to supply only 85% of total protein requirements) mixture
of ground corn and toasted SBM (LTSBM). Dietary regimes were
composed of wheat (Triticum aestivum L.) silage and either C
or F, and one of the 3 protein supplements. Two Jersey
steers fitted with permanent ruminaI cannulae were fed 25%
wheat silage and either C or F to evaluate the degradability
of dietary components in situ.
Dietary fat decreased intake of DM, CP, NDF, ADF,
hemicellulose and cellulose, and increased digestibility of
CP and gross energy. Digestibility of ADF and cellulose,
yield of milk and milk fat, SNF, CP, and lactose were also
decreased in cows fed F. Digestibility of CP was 67.5, 64.3,
and 71.4% for TSBM, LTSBM and SBM. Protein treatments did
not affect milk production or composition. Effective
degradability of CP was 60.0, 31.6 and 26.6% for SBM, LTSBM

---

63
and TSBM, respectively. Results suggest that decreased milk
protein content in cows receiving fat is not a result of
inadequate protein supply.
KEY WORDS: dietary fat, toasted soybean Meal, protein
solubility, protein level, milk production, milk proteine
INTRODUCTION
Several reports have indicated that the addition of
lipids to diets for lactating cows May cause a decline in
milk prote in percentage or yield (3, 4, 18, 23). Although
several hypotheses have been proposed to explain this
phenomenon, none appears to be satisfactory at this time. It
has also been reported that dietary fat frequently increases
yield of milk '(15) and milk fat (4, 18, 23) without
necessarily reversing the weight loss usually observed
during the first 6 to 8 weeks of lactation. An increase in
milk production is normally accompanied by an increased
synthesis of lactose. It is possible that under conditions
in which fat is fed, there is a greater need for glucose
from gluconeogenesis. If so, there May also be a greater
need for metabolizable proteine Furthermore, post-ruminaI
administration of sodium caseinate and other proteins have
increased milk protein concentration (14, 22).
This study was designed to evaluate: a) the effects of
rumen escape prote in (REP) and dietary fat on milk yield,
milk composition and nutrient digestibility b) the response
of lactating dairy cows to low protein supplementation when

---

64
fed a diet with high REP potential, and c) the influence of
heating SBM on the in situ disappearance of DM and CP from
nylon bags.
MATERlALS AND METHODS
Twelve Holstein cows in mid-lactation were selected
for a production trial and two Jersey steers fitted with
permanent ruminaI cannulae were selected to evaluate the
degradability of silage, diets and protein supplements in
situ.
Production trial: Cows were blocked into two groups of
6 according to production and days in milk (DlM). Blocks of
cows were assigned at random to one of two 3x3 Latin
Squares; cows in square one received a control concentrate
with no added fat (C) while cows in square two received a
concentrate containing 9.3% fat (F). Yellow grease provided
the fat in F. Concentrate F was fed to provide approximately
4% of the total DM as fat. Cows were fed their respective
concentrate diet (table 1) 4 times daily using a BOUMATlC
computerized feeder with two feeding stations. Wheat
(Triticum aestivum L.) silage was fed once daily to supply
120% of the maintenance energy requirements or 11.6 Mcal
NEL. Sodium bicarbonate and a trace mineraI mix were
provided ad libitum. Each square was arranged to include
three 21-d periods, three sub-blocks of 2 cows each and
three protein supplements: a) 2.3 kg/d of solvent-extracted
soybean meal (SBM or high protein, high solubility

---

65
supplement), b) 2.3 k9/d toasted SBM (TSBM, or high-protein,
low solubility supplement) or c) 2.3 k9/d of a mixture of
ground shelled corn and TSBM (LTSBM, or low protein, low
solubility supplement). Protein supplements were fed to
complete the silage and concentrates in supplying 100% (SBM
and TSBM) or 85% (LTSBM) of NRC (9) CP requirements for
maintenance and production. Protein supplements were fed
top-dressed on the silage through CALAN gates. Treatment
combinations resulting from level of fat by prote in
treatment were as follow: a) C plus SBM; b) C plus TSBM; c)
C plus LTSBM; d) F plus SBM; e) F plus TSBM; and f)
F plus
LTSBM.
Solvent-extracted SBM was toasted on metal pans
measuring approximately 74 by 49 cm wide and 5 cm deep. The
SBM was spread to cover aIl pan surface to an average
thickness of 2.5 cm. Pans containing the SBM were placed on
the shelves of a GRIEDE forced air oven and heated at 1490 C
for 4 h (12).
Diets, silage, and orts were sampled daily to
determine DMI. Cow body weights were determined during the
last 3 d of each periode Cows were milked twice daily and
milk was sampled twice daily during the last 7 d of each
periode Milk was preserved with 1 ml of 10% formaldehyde and
stored at 40 C until analyzed.
Fecal grab samples were collected at 0800, 1000, 1200,
1400, 1600 and 1800 h during d 15, 16, 17, 18, 19 and 20,
respectively, of each 21-d periode Fecal samples were dried

---

66
at 600 C for 5 d, ground through a 1 mm Wiley mill screen
and composited. Samples of concentrate diets, protein
supplements, silage and orts were dried at 60 0 C for 3 d.
All solid samples were ground through a 1 mm Wiley mill
screen and composited.
Solid samples were subsequently analyzed for ether
extract by soxhlet, for gross energy and ash according to
AOAC (1) and for neutral and acid detergent fiber, cellulose
and lignin as described by Robertson and Van Soest (19). All
crude protein determinations were performed on a Technicon
Model II Autoanalyzer after digestion on a block digester.
Acid detergent insoluble nitrogen (ADIN) was determined by
submitting residue of ADF extraction (6) to a N
determination as described. Total milk solids were
determined in duplicate by lyophilizing 10 ml of milk in
Gooch crucibles on a Labconco model 75040 freeze dryer. Milk
fat was determined by Babcock (1).
Percentage silage remaining in the orts was calculated
using CP and NDF content of orts, silage and protein
supplements as markers; NEL intake was estimated using NRC
(10) values for feed ingredients, and microbial CP (MCP)
production was predicted using NEL content of feed
ingredients as described in NRC (10). Metabolizable protein
(MP) was calculated as the sum of REP and MCP.
Apparent digestibility coefficients were determined
using ash-free indigestible acid detergent fiber (IADF) as a
marker. IADF was determined on orts and fecal samples using

---

67
Near Infrared Reflectance Spectroscopy (NIRS)
(Windham et
al, unpublished). For samples of (1) silage, concentrates
and prote in supplements and (2) orts and feces for which
IADF values were rejected as outliers by NIR, 2 gm of each
sample were incubated in duplicate in vitro for 120 h as
described by Tilley and Terry (24). In vitro sample residue
and media were then filtered through ADF crucibles and
residue was submitted to an ADF digestion as described
previously.
Statistical analysis was performed using SAS (20)
general linear models; Effect of protein treatment by level
of fat combinat ions was analyzed using the following model:
Y"k
1.)
= u + F' +
1 .S'
+
)
Pk + F*S + F*P + E' 'k
1.)
,
where Yijk is the variable of interest, F is the level of
fat, S is the protein supplement, P is the period,
F*S is
the level of fat by protein supplement interaction and F*P
is the level of fat by period interaction. Main effects of
protein solubility (PS) and protein level (PL) were also
analyzed, using the model:
Yijk = u + Fi + Zj + Lk + Pl + F*Z + F*L + F*C +
Eijkl'
Where Z is PS, L is PL and F*C is level of fat by cow
interaction. Effect of block was assumed to be negligible.
Degradability study: Jersey steers were randomly
assigned to a complete mixed diet containing wheat silage
(25% of DM) and either C or F to determine the degradability
of DM and CP from concentrates, prote in supplements and

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68
silage. Feed was offered at 110% of maintenance DM
requirements for 10 d prior to the beginning of the study.
AlI feeds were ground through a 2 mm screen and a
sample of approximately 5 gm (air dry) was placed in nylon
bags. Bags were made of nylon cloth with an average mesh
size of 48 ~m as described by Kirkpatrick and Kennelly (8).
Final bag size exposed to ruminaI fermentation was
approximately 10 x 7 cm. sixteen bags were prepared for each
concentrate and 30 bags for silage and each protein
supplement, to allow for zero time measurements and for
incubation periods of l, 3, 6, 9, 12, 18 and 24 h. Bags
containing C were incubated in the rumen of the steer fed C,
bags of F in the steer fed F and bags of aIl other diet
components in both steers. Nylon bags were placed in the
ventral sac of the rumen on d 9 at 1100 h.
At the end of each incubation time, 2 bags of each
diet were removed randomly from each steer and washed under
running tap water until the rinsing water was colorless
(approximately 3 min). For each diet, zero time samples were
washed as described to provide 0 h values. Washed bags were
dried at 600 C in a forced air oven for 72 h. Bags were then
weighed to determine residual DM. Samples of bag DM residue
were analyzed for CP as described.
The percentage DM and CP disappearance at each
incubation time was calculated from the amount remaining
after incubation. The disappearance rate was fitted to the
following equation (14):

---

69
P = a + b (l-e-kt ),
where P = disappearance rate at time t, a = an intercept
representing the portion of DM or CP solubilized, b = the
fraction of DM or CP that will be degraded if given
sufficient time for digestion in the rumen, k = rate
constant of disappearance of fraction b, and t = time of
incubation. Nonlinear parameters a, band k were estimated
by an iterative least squares procedure (20), and best-fit
values were chosen using the smallest sums of squares after
10 iterations. Disappearance from nylon bags does not
provide a direct estimate of actual degradability since time
spent in the rumen affect affects extent of ruminaI
degradation. Estimates of effective degradability of DM
(DOM) and CP (DCP) in the rumen were calculated using the
following equation (14):
DOM or DCP = a + [(bxk)/(k+r)],
where r is the estimated rate of outflow from the rumen. For
the purpose of this study, a solid outflow rate of .05/h (8,
13) was utilized based on observations by Eliman and ~rskov
(5) and by Kirkpatrick and Kennelly (8) that under normal
feeding conditions protein source does not affect flow rate.
Parameters included in the statistical analyses were:
percentage DM or CP disappearance from nylon bags, DOM and
DCP. Comparisons were made between concentrate diets (C vs.
F), between protein supplements (SBM vs. TSBM vs. LTSBM) and
for each individual feed other than C and F, between samples
in C vs. samples in F.

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70
RESULTS AND DISCUSSION
Lactation trial: Pretrial measurements indicated that
cows blocked in squares 1 and 2 averaged 30.6 and 30.4 kg
milk/d and 167 and 171.5 DIM, respectively. Cows in the 3
sub-blocks of latin square 1 averaged 31.6, 30.1 and 30.0
kg/d milk and 147, 196 and 159 DIM; cows in square 2
averaged 30.5, 30.1 and 29.2 k9/d milk and 172, 174 and 196
DIM. There was no difference in milk production or DIM
between blocks or sub-blocks initially (P>.05).
Ingredient and partial nutrient compositions of diets
are listed in table 1. The ADIN content of SBM was increased
33.3% due to heating. The addition of 9.3% fat to the
control concentrate increased NEL density by 19.9% and
depressed dry matter intake by 8.1% (P<.OOl) and CP intake
by 10.9% (P<.09)
(table 2). silage intake was also higher
(P<.OOl) for cows fed C. Although dietary fat has lowered
dry matter intake in other studies (23), milk yield and milk
fat were not depressed because of the higher calorie density
of fat-containing diets. In a previous study,
(11) cows
receiving fat maintained DM and CP intakes similar to the
control diet; gross energy intake was increased, NEL intake
was 7.5% greater than for the control diet, and cows fed fat
produced more milk and milk fat. In the current study, CP
and DM intakes were reduced.
Intake of CP was lower (P<.OOl) in cows fed low
solubility protein; CP intake was also higher (P<.OOl) in
cows fed higher levels of CP. Intake of REP was highest with

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71
cows fed TSBM; LTSBM and SBM provided the same amount of
REP; Estimates of MCP production and MP were both higher for
F-LTSBM than for F-SBM; estimates of MP yield must be
considered carefully since the prediction equation (10)
allows for considerable error; aIl protein supplements
appear to have provided more MP than recommended by the NRC.
Intake of NDF and hemicellulose was higher (P<.02 and
P<.001) with toasted SBM than with unheated SBM; this may be
a result of some of the CP being bound to NDF components as
a result of heat treatment. Intake of DM as a percentage of
body weight was lower (P<.001) in cows receiving F,
indicating that body size was not a factor. Weight gain was
not affected by fat, PS or PL. However, cows fed F-LTSBM
gained more weight than cows fed C-SBM and F-SBM.
Digestibility of CP and gross energy were increased
whereas digestibility of ADF and cellulose were decreased by
fat (table 3). Increased digestibility of CP due to fat
addition has previously been observed by Palmquist and
Conrad (15), and by Nianogo and Amos (unpublished). Although
CP digestibility has not changed in other reports (16), it
is possible that high levels of fat might allow physical
coating of the protein, decreasing its digestibility in the
rumen. Cows on a higher level of CP had higher digestion
coefficients for CP, NDF and hemicellulose. Apparent
digestion coefficients of CP were highest with SBM (P<.02)
and lowest with LTSBM. Digestion coefficients for
hemicellulose were higher (P<.004) with high REP diets;

---

72
intake of hemicellulose may have been inflated due to
nitrogen binding to hemicellulose during the heat treatment
of SBM; digestion of some of the Maillard reaction products
would contribute to apparently higher digestion values for
hemicellulose. Fecal CP increased with toasted SBM (P<.Ol)
and tended to increase (P<.07) with higher levels of CP.
Higher fecal CP observed with toasted SBM may be due to
higher levels of ADIN resulting from heat treatment.
Milk yield was reduced (P<.06) and milk concentration
and yield of fat and SNF were depressed in cows fed fat
(table 4). Decreased milk yield with fat feeding has
occurred in other studies (16) and may be due to lower DM
consumption by cows fed F. Dietary fat also caused the
percentage of milk ash to increase and yield of milk lactose
to decrease. with cows fed unheated SBM, dietary fat tended
to depress both milk protein percentage (5.7%) and yield
(10.6%). This was less apparent with cows fed either level
of TSBM. There was no effect of PS or PL on milk yield or
composition. However, restricting protein intake of cows to
only 85% of their total requirements increased the
efficiency of milk prote in production (kg milk CP/kg CP
intake) by 50%.
Effect of REP on milk protein production has not been
consistent. Henderson et al (7) found that increased intake
of REP from extruded SBM increased milk protein production
by 6.7 to 10.6%, depending on diet serving as control.
Shingoethe et al (21) found that milk CP percentage was

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73
decreased in cows fed SBM heated by extrusion, however
intake of CP was not reported.
Degradability study: Disappearance of DM and CP as
affected by protein supplement and effective degradability
of DM (DDM) and CP (DCP) from diets are in table 5.
Disappearance of DM and CP for protein supplements are shown
on figure 1 (DM) and 2 (CP). Disappearance of DM and CP was
greater for SBM than for LTSBM and TSBM (table 5, figures 1
and 2).
Crude prote in from TSBM and LTSBM was released at
similar rates. Mean disappearance (based on data from aIl 3
supplements) of DM was greater when incubated in the steer
fed F (P<.OOOl)i disappearance of DM and CP of concentrate
diets was not affected by level of fat. Increased
disappearance of DM in F is not consistent with our in vivo
resultsi however, disappearance from nylon bags is solely
based on rumen activity, while in vivo results reflect
overall gastrointestinal digestion. AlI interactions related
to disappearance from bags were significant, indicating that
the main effects of time, protein treatment and level of fat
are interrelated in their influence on DM and CP
disappearance. Interaction between treatment and time is
apparent in (figure 1 and 2).
Due to the presence of about 51% ground corn in LTSBM,
disappearance of DM from LTSBM tended to be greater than
that in TSBM during the first 1 to 3 h of incubation.
Whereas disappearance of DM remained greater for TSBM than

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74
for LTSBM for incubation times greater than 6 h. Effective
degradability of CP was greater for SBM (P<.OOOl) than for
LTSBM and TSBM. DCP values for SBM were similar to those
obtained by Broderick et al (2). Broderick et al (2) have
questioned the validity of in situ methods for estimating
the degradability of very slowly degradable protein sources.
It was found using a flow rate of .05/h that degradability
values obtained in situ were only 83% of those obtained in
vitro. These lower values for in situ estimates were
attributed in part to higher values of zero time CP
disappearance.
Additionally, DCP was greatest for silage probably due
to higher ammonia content.-For most components, effective
degradability of DM and CP were or tended to be lower with F
than with C. DOM was 4.4% and DCP 2.0% greater for C than
for F when samples of each concentrate were incubated in
steers fed the concentrate of interest.
CONCLUSION
It appears that feeding unprotected dietary fat may
not be beneficial unless DMI is maintained at a normal
level. Decreased fiber digestion due to toxic effects of
fatty acids on rumen microbes contributes to decreased milk
fat (17, 25). Feeding a protein source with higher REP may
alleviate some of the negative effects associated with
dietary fat. Heating SBM at 1490 C for 4 h appears to double
the REP potential of SBM. In situ and in vitro degradability
studies are useful tools allowing the prediction of actual

---

75
REP intake and expected MCP yield. Results of the production
trial indicated that metabolizable prote in requirements of
cows in mid lactation may be met with lower CP levels when
protein supplements high in REP are fed.
Milk production
was not altered and efficiency of milk prote in production
was increased with the low protein high REP diets.

---

76
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77
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79
23.
Storry, J.E., P.E. Brumby, A.J. Hall, and V. w.
Johnson. 1974. Response of the lactating cow to
different methods of incorporating case in and coconut
oil in the diet. J. Dairy Sci. 57:61.
24.
Tilley, J. M. and R. A. Terry. 1963. A two-stage
technique for the in vitro digestion of forage crops.
J. British grassland Soc. 18:104.
25.
Van Soest, P. J. 1963. Ruminant fat metabolism with
particular reference to factors affecting low milk
fat and feed efficiency. A review. J. Dairy Sci.
46:204.

---

ao
FOOTNOTES
1Boumatic Dairy Equipment Co. A division of D.E.C., Inc.
2American Calan, Inc. P. O. Box 307, Jenness Pond Rd.
Northwood, NH 03261.
3Griede Corp. Round Lake, Il 60073.
4Specifications for the Technicon Autoa~alyzer II
Continuous-flow Analytical Instrument (Technical
Publication No. TSO-0170-2). 1975. Technicon
Instruments Corp. Tarrytown, NY
5Labconco Freeze Dryer Model 75040. Kansas City, MO.

---

81
Table 1. Ingredient composition and partial compositional
analyses of diets fed lactating dairy cows (DM basis).
Concentrate
Prote!n Supplement
Control
Fat
SBM
LTSBM
TSBM
Silage
----------------------t---------------------
30.3
21.0
51.0
Corn
1. 9
100
SBM
49.0
100
TSBM
25.3
23.4
CSH
22.7
soyhulls
22.7
CGF
20.2
20.2
Fat
9.3
Dical
.5
.5
Limestone
1.0
1.0
Dry matter
89.7
91.1
88.4
93.0
99.8
32 .8
Crude protein
19.6
18.2
73.7
39.6
72.1
14.4
Undegradability
of Cpb
48.1
49.1
40.0
73.4
68.4
24.2
NDF
48.4
45.4
18.0
37.5
54.2
59.2
ADF
24.4
22.2
5.7
5.7
6.6
32.3
Cellulose
20.3
18.8
5.5
4.8
5.7
27.0
Hemicellulose
23.9
23.2
12.3
31.9
6.8
26.9
Lignin
4.2
3.4
.7
1.1
1.1
4.2
ADIN
.6
.8
Ether extract
6.7
14.3
3.4
7.8
3.0
2.5
Ash
6.8
6.4
8.2
8.1
5.2
5.4
------------------Mcal/kg------------------
Gross energy
3.5
4.0
4.5
4.2
4.3
4.2
NELc
1.6
1.9
1.9
2.0
1.9
1.4
aSBM: soybean meal; LTSBM: mixture of ground corn and toasted
SBM; TSBM: toasted SBM; CSH: cottonseed hulls; CGF: corn
gluten feed; ADIN: acid detergent insoluble nitrogen.
bAs calculated from in situ study.
cCalculated from NRC (1978).

---

Table 2. Nutrient intake and body weight change of lactating cows as influenced by fat
addition, and level of protein and rumen escape protein.
Dieta
Main EffectD
ITEMc
C-TSBM
F-TSBM
C-LTSBM
F-LTSBM
C-SBM
F-SBM
Fat
PS
PL
SE
----------------------- kg/d----------------------
Intake:
DM
17.5d
16.18f
17.2d
16.6def
17.7d
15.4 e
.001
NS
NS
.24
Silage
6.6d
5.3 e
6.6d
5.0e
6.9d
4.4 e
.001
NS
NS
.26
CP
3.1 d
2.Be
2.6 f
2.4g
3.1h
2.7 e
.09
.001
.001
.06
REP
1.6d
1. 58
1.2 fh
1.19 f
1. 2h
1.1g
.005
.001
.001
.04
NDF
9.2 d
B.3 e
B.7de
B.1 ef
B.Bde
7.5de
.001
.02
NS
.27
ADF
4.5dfg
4.1 8
4.5 f g
4.2 fe
4.6g
3.ge
.001
NS
NS
.OB
Hemicell.
4.4 d
3.98
4.2 de
4.0e
3.ge
3.3 f
.001
.001
NS
.OB
Cellulose
3.9df
3.4 8
3.Bf
3.5e
4.0 f
3.3 e
.001
NS
NS
.OB
GE, .Mcal/d
70.5
70.0
70.1
71.B
71.0
67.0
NS
NS
NS
.9B
NELl , Mcal/d
27.8d8
2B.36de
27.9de
29.4 d
27.9de
27.3 e
NS
NS
NS
.31
------------------------ ,-----------------------
DM, , Bwi
3.0d
2.6e
3.0d
2.6 e
3.0d
2.5e
.001
NS
NS
.05
--------------------------kg----------------------
Body weight
596
635
593
639
597
633
.001
NS
NS
B.BO
W8iyht gaink
1.5de
1.7de
.1de
10.1d
-1.4 8
-5.1 e
NS
NS
NS
.02
MCP
1.8de
1.8de
1.8de
1.9d
1.Bde
1. Be
NS
NS
NS
.002
MP
3.6de
3.7de
3.6de
3.8d
3.6de
3.5e
NS
HS
HS
.003
aC: control: F: control plus 4' fat: SBM: soybean Meal: TSBM: toasted SBM; LTSBM: low
protein mixture of TSBM and ground corn; PS: protein solubility (low vs high); PL:
protein level (high vs low).
bprobability of significance of main effects from the analysis of variance.
cDM: dry matter; REP: rumen escape protein; hemicell.: hemicellulose; GE: gross energYi BW:
~ody weight: MCP: microbial CP; MP: metabolizable CP ;
defghMeans in the same row with no common superscript differ at P<.Ol (REP, fecal CP) and
p<.n1 (other).
i NEL calculated based on HRC (1978). MCP calculated using NEL values (HRC, 198B).
jpercentage dry matter intake relative ta body weight.
~otal body weight change in kg.
(Xl
l\\)

---

Table 3. Nutrient digestibility and fecal CP of lactating cows as influenced by fat
addition, and level of protein and rumen escape protein.
DietCl
Main Effectl:>
ItemC
C-TSBM
F-TSBM
C-LTSBM
F-LTSBM
C-SBM
F-SBM
Fat
PS
PL
SE
-----------------------%-------------------------
Dry matter
60.S d
56.Se
5S.3de
59.7de
59.9d
60.7 d
NS
NS
NS
1.14
CP
67.4 d
67.5d
62.2 e
66.4 d
69.2 d
73.6 f
.01
.02
.05
3.1S
NDF
59.2 d
56.0e
54.5e
54.g e
56.Se
55.4 e
NS
NS
.03
2.77
ADF
53.6d
49.1 e
51.9d
49.4 e
52.Sd
49.2 e
.001
NS
NS
2.92
Hemicell. c
63.6df
60.9 fh
57.3 e g
60.6 f g h
56.Se
57.geh
NS
.004
.04
2.S3
Cellulose
63.Sdf
56.4 e
61.0 f
57.2 e
63.1 f
57.3e
.001
NS
NS
2.42
GE
74.6de
74.4 de
72.7 d
75.5 e
74.3de
76.2 e
.03
NS
NS
1.42
-----------------------kgjd.-----------------------
Fecal CP
1.0d
.ge
1.0de
.Sf
1.0de
.7 f
.001
.01
.07
.06
aC: controli F: control plus 4% fati SBM: soybean meali TSBM: toasted SBMi LTSBM: low
protein mixture of TSBM and ground corni PS: prote in solubility (low vs high)i PL:
prote in level (high vs low).
bprobability of significance of relevant main effects from the analysis of variance.
cHemicell.: hemicellulosei GE: gross energYi
defghMeans in the same row with no common superscript are significantly different
at P<.05 (ADF and hemicellulose), P<.04 (dry matter and NDF), at P<.02
(cellulose and gross energy)
for CP, C-TSBM is different from F-TSBM (P<.Ol),
from C-LTSBM (P<.OOOl), from F-LTSBM (P<.OOOl) and from F-SBM (P<.OOOl).
(»
loi

---

Table 4. Milk and milk composition of lactating dairy cows as affected by treatment
combinat ion.
Dieta
Main EffectsD
Item
C-TS8M
F-TS8M
C-LTS8M
F-LTSBM
C-SBM
F-SBM
Fat
PS
PL
SE
Percentage:
Solids
12.7 Cd
12.2 ce
12.6cde
12.2ce
12.7d
12.1e
.001
HS
HS
.10
Fat
3.2cd
3.0 cd
3.3 cd
2.9d
3.3 c
3.0cd
.001
HS
HS
.06
SHF
9.4
9.2
9.3
9.4
9.4
9.1
HS
HS
HS
.06
CP
3.2
3.2
3.2
3.2
3.3
3.0
HS
HS
HS
.06
Ash
.7cd
.ad
.7 c
.ad
.7 c
.acd
.004
HS
HS
.01
Lactose
4.7
4.4 d
S.2 c
4.7 c
4.6 c
4.6c
HS
HS
HS
.14
kgjd:
Milk
23.1
2l.7
23.2
2l.1
23.4
2l.a
.002
HS
HS
.43
Fat
.7 c
.6d
.ac
.6d
.Sc
.7d
.0001
HS
HS
.02
Protein
.9
.7
.7
.7
.a
.7
.02
HS
HS
.02
SHF
2.2
2.0
2.2
2.0
2.2
2.0
.001
HS
HS
.04
Lactose
l . lcd
l.Od
l.2 c
l.Od
l . l c
l.Od
.07
HS
HS
.03
MPPIf
.2g
.2g
.3 h
.3h
.2g
.3g
HS
HS
.001
.04
aC)
control: F: control plus 4\\ fat; S8M: soybean meal; TSBM: toasted SBM; LTSBM: low
protein mixture of TS8M and ground corn.
bprobability of significance of relevant main effects from the analysis of variance.
cdeMeans in the same row with no common superscript are significantly different at
P<.OS.
fMilk CP (kg): CP consumed (kg).
ghMeans in the same row with no common superscript are significantly different at P<.Ol.
co
"'"

---

Table 5. In situ disappearance and effective DM and CP degradability of
diets.
Diet Componenta
Itema
Conc.
SBM
LTSBM
TSBM
Silage
SE
-----------------%------------------
Disappearanceb :
54.6d
32.6 f
DM
32.9c
37.7 e
36.4
1. 64
CP
46.9 c
53.9d
30.2e
28.8 f
73.8
1. 61
Degradabilitye:
43.8 cd
47.7 cd
52.9d
48.0d
DDM
21.9 c
4.70
DCP
51.4 c
60.0ce
31.6d
26.6d
75.8 e
6.90
aConc: concentrates; SBM: soybean meal; TSBM: toasted SBM; LTSBM: low
prote in mixture of TSBM and ground cOrn.
bMean disappearance from nylon bags corresponding to an average time
of 9.125 h.
cMean effective degradability of DM (DDM) or CP (DCP), calculated as
indicated by Orskov and McDonald (1979);
cdefMeans in the same row without a common superscript differ
(P<.OOOl).
(»
U1

---

---

87
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---

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---

INFLUENCE OF DIETARY FAT, PROTEIN SOLUBILITY AND CALVING
SEASON ON VOLUNTARY FEED INTAKE, NUTRIENT DIGESTIBILITY,
MILK YIELD AND COMPOSITION1.
1Nianogo, A.J., H.E. Amos, and M.A. Froetschel. To be
submitted to Journal of Dairy Science.
90

---

91
ABSTRACT
Two Jersey steers fitted with permanent ruminaI
cannulae were fed 25% wheat silage and either a control
concentrate (C) or a concentrate with 12.1% fat (F) to
evaluate the degradability of silage, C, F and 2 prote in
supplements. Twelve summer calving (SC) and 12 fall calving
(FC) multiparous Holstein cows were blocked into 4 groups to
determine the effect of calving season, dietary fat and
protein solubility on milk production. Blocks were randomly
assigned to one of 4 dietary treatment combinations: a) C
plus SBM as high solubility protein (HSP) supplement; b) C
plus a mixture of toasted SBM and corn gluten meal as low
solubility protein (LSP) ,supplement; c) blend of C with F to
provide 1 kg/d fat, plus HSP; d) blend of C and F plus LSP.
Cows were allowed up to 18.1 kg/d of their respective
concentrate and received wheat silage ad libitum. Nutrient
intake, milk yield and composition, body weight changes were
monitored during 16 weeks. Daily ambient temperature
readings were obtained from the local weather station.
In
situ disappearance of DM was highest for HSP and lowest for
LSP. Effective degradability of CP was 61.2, 64.6, 25.1 and
75.8% for concentrates, HSP and LSP and silage,
respectively. DM intake was not affected by level of fat,
prote in solubility or calving season. Digestibility of DM
and fiber components were increased by feeding fat. Milk
concentration and yield of fat, SNF and protein were higher
in FC than in SC cows. Milk yield and composition were not

---

92
affected by level of fat or by protein solubility. At high
concentrate intake, calving season had more effect on milk
production than level of fat or protein solubility.
KEY WORDS: Dietary fat, protein solubility, calving season,
dry matter intake, milk production, milk composition.
INTRODUCTION
Because of the increased energy requirement of dairy
cows in early lactation, dietary fat is a convenient
ingredient to help increase energy intake. However, several
studies have reported a decrease in milk protein content due
to dietary fat (3, 5, 7, 11, 22, 26). It has been suggested
that milk protein content increases as intake of glucogenic
substrates increases (8). Increasing the flow of preformed
degradable protein to the abomasum has increased milk
protein production in some studies (25, 29); Spires et al
(29) and ~rskov et al (18) observed an increase in milk
protein percentage and yield in cows infused post ruminally
with sodium caseinate. However, decreased milk protein
production with rumen escape proteins (REP) has also been
reported (2), particularly when corn-based proteins were
used. Schawb et al (27) have shown that lysine and
methionine are likely to be the first limiting amine acids
with corn based diets. There is need for additional
information on interaction between dietary fat and protein
nutrition in lactating dairy cows.

---

93
Dairy cows in warmer climates including the Southern
United states are submitted to ambient temperatures often
exceeding the upper critical temperature of animaIs during
major portions of the day. Such temperatures are not
favorable to intensive production as they increase
maintenance energy requirements, while at the same time
decreasing dry matter intake (4).
Chandler (6) indicated
that dairy cattle in warmer climates may observe a 2.3 to
4.5 kg drop in milk production and a decline in milk fat
test during the months of July through September. This
corresponds to an annual potential income loss of $13,000.00
per 100 cows (6).
This study was designed to investigate 1) the
degradability of DM and CP from protein sources and other
dietary components in situ; 2) effects of REP and dietary
fat on nutrient intake and digestibility, milk yield and
milk composition of Holstein cows in early lactation; and
3) the effect of calving season on nutrient intake and
digestibility, milk production and composition.
MATERIALS AND METHODS
Two Jersey steers fitted with permanent ruminaI canulae
were selected to evaluate the degradability of dietary
components in situ. Twenty-four multiparous Holstein cows
with an average annual production of 9,266 kg of ME milk on
a 305-d basis were selected for a production trial.

---

94
Degradability study: Two rumen cannulated Jersey steers
were randomly assigned to a complete mixed diet containing
wheat silage (25% of DM) and either a control concentrate
with no added fat (C) or a concentrate containing 12.1%
added fat (F).
Steers were fed to determine the
degradability of DM and CP from concentrates, protein
supplements and silage.
Yellow grease provided the fat in
F.
Solvent extracted soybean meal (SBM) was used as a high
solubility protein (HSP) and a mixture of toasted SBM and
corn gluten meal (table 2) was used as a low solubility
protein (LSP). To obtain toasted SBM, SBM was spread on
metal pans at an average thickness of 2.5 cm; pans were
placed in a forced air oven and heated at 1490 C for 4 h
(17). Steers were fed at 110% of maintenance DM requirements
and allowed 10 d of adjustment prior to the beginning of the
study.
AlI feeds were ground through a 2 mm screen and a
sample of approximately 5 gm (air dry) was placed in nylon
bags. Bags were made of nylon cloth with an average mesh
size of 48 ~m as described by Kirkpatrick and Kennelly (10).
Sixteen bags were prepared for each concentrate and 30 bags
for silage and each protein supplement, to allow for zero
time measurements and for incubation periods of 1, 3, 6, 9,
12, 18 and 24 h. Bags containing C were incubated in the
rumen of the steer fed C, bags of F in the steer fed F and

---

95
bags of aIl other diet components in both steers. Nylon bags
were placed in the ventral sac of the rumen.
The percentage DM and CP disappearance at each
incubation time and the effective degradability of DM and CP
was calculated using a flow rate of .OS/h, as described by
~rskov and McDonald (18) and by Kirkpatrick and Kennelly
(10). Parameters included in the statistical analyses were:
percentage DM or CP disappearance from nylon bags, and
effective degradability of DM and CP.
Lactation study: 12 summer calving (SC) and 12 fall
calving (FC) multiparous cows were blocked into 4 groups
based on their 305 d, 2X, ME milk production from the
previous lactation. Each block included 3 SC and 3 FC cows.
Characteristics of trial cows are shown in table 1. Blocks
were randomly assigned to one of 4 di~tary treatment
combinations: 1) C plus HSPi 2) C plus LSPi 3) blend of C
and F (BCF) to provide an intake of 1 k9/d fat, plus HSPi 4)
BCF plus LSP. Intake of protein supplement was adjusted
weekly, based on the previous week milk production. Maximum
intake of feeds other than silage was limited to 18.1
kg/day.
Cows were trained to use CALAN gates prepartum and were
weighed and introduced to the study 1 d postpartum. Each cow
was fed wheat silage and protein supplement individually
using CALAN gates and the respective concentrate in 4 equal
intervals through a BOUMATIC feeder with 2 feeding stations.
Sodium bicarbonate and a trace mineraI mix were provided ad

---

96
libitum. The study was divided into four 4 wk periods: the
first period was further subdivided into 2 sub-periods of 2
wk each. Diets, silage, and orts were sampled daily to
determine DMI. Mean body weights of cows were determined on
d 11, 12, and 13, and
again on d 25, 26 and 27 during each
periode Cows were milked twice daily and milk was sampled
twice daily during the last 7 d of each sub-period and
periode Milk was preserved with 1 ml of 10% formaldehyde and
stored at 4 Oc until analyzed. Daily temperature readings
were obtained from the local weather service.
Fecal grab samples were collected at 0800, 1000, 1200,
1400, 1600 and 1800 h during d 8, 9, 10, 11, 12 and 13 of
sub-periods and during d 22, 23, 24, 25, 26 and 27 of each
period, respectively. Fecal samples were dried at 60 0 C for 5
d, ground through a 1 mm Wiley mill screen and composited.
Samples of concentrates, protein supplements, silage and
orts were dried at 60 0 C for 3 d. AlI solid samples were
ground through a 1 mm Wiley mill screen and composited.
Solid samples were analyzed for ether extract by
soxhlet (1), for gross energy and ash according to AOAC (1)
and for neutral and acid detergent fiber, cellulose and
lignin as described by Robertson and Van Soest (23). AlI
crude protein determinations were performed on a Technicon
Model II Autoanalyzer after digestion on a block digester.
Total milk solids were determined in duplicate by
lyophilizing 10 ml of milk in Gooch crucibles on a Labconco

---

97
..
model 75040 freeze dryer. Milk fat was determined by the
Babcock method (1).
Apparent digestibility coefficients were determined
using ash-free indigestible acid detergent fiber (IADF) as a
marker. Orts and fecal samples were analyzed for IADF using
Near Infrared Reflectance Spectroscopy (NIRS) Windham et al,
unpublished). For samples of (a) silage, concentrates and
protein supplements and (b) orts and feces for which IADF
values were rejected as outliers by NIRS, 2 gm of each
sample were incubated in duplicate in vitro for 120 h as
described by Tilley and Terry (32). In vitro sample residue
and media were then filtered through ADF crucibles and
residue was submitted to an ADF digestion (9).
Microbial crude protein (MCP) yield was estimated as
indicated by NRC (16), using NEL values for consumed feed
ingredients (14). Statistical analysis was performed using
SAS (24) general linear models; The model used for the
analysis was:
Yijk = Fi + Pj + Sk + F*P + F*S + p*s + F*P*S + Eijk;
Where Yijk represents observations, BCF the effect of fat, P
the effect of protein solubility and S the effect of calving
season. Treatment means were separated using the t test
(30) •
RESULTS AND DISCUSSION
In situ study: Disappearance and effective
degradability data are summarized in table 3. Disappearance

---

98
of DM was highest for SBM and lowest for the LSP mix. CP
disappearance was highest for silage and lowest for the LSP
mix. Effective degradability of CP were 61.2, 64.6, 25.1 and
75.8% for concentrates, HSP, LSP and silage, respectively.
Effective degradability of CP for SBM (HSP) was similar to
values reported by the NRC (16); degradability of the
toasted SBM-corn gluten mix (LSP) was slightly lower than
expected (16). Results indicate that LSP provided 61.2% more
(P<.05) REP and 32.3% more rumen escape DM than HSP.
Lactation study: Data on 2 cows were not used in the
statistical analyses due to displaced abomasum in one case
and to mastitis in another. Ingredient composition and
partial compositional analyses of dietary components are
shown in table 2. Concentration of NEL and ether extract
were increased 21.1% and 11.3%, respectively, by fat
addition. Nutrient intakes are reported in table 4 for main
effects. Main effect influence on DMI is shown in figure 1.
Dry matter intake was not affected by fat addition, protein
solubility or calving season.
Intake response of dairy cows to dietary fat has been
inconsistent; DMI has decreased with unprotected sources of
fat (31), increased with unprotected coconut oil (11) and
protected fat (28, 31). Maximum DMI in the present study
occurred during week 12 and 14 for LSP and HSP and during wk
12 and 14 for C and BCF, respectively (figure 1). High fat
diets have caused maximum DMI to occur up to 5 wk earlier in
other studies; maximum DMI recorded by smith et al (28)

---

99
occurred at wk 9 and 14 for control and fat containing
diets, respectively.
Maximum dry matter intake occurred during week 10 for
FC and during week 15 for SC cows (figure 1). Average
ambient temperature during peak DMI was 7.26 and 12.89 Oc
for FC and for SC, respectively (figure 4B). SC cows were
exposed to average daily temperatures greater than 25 Oc for
the first 5 weeks of lactation. Beede and Collier (4)
suggested that DMI of feedlot and dairy cattle begins to
decline at 25 to 27 oC. However, NRC (15) suggested that
with lactating dairy cows, DMI declines more rapidly when
the roughage content of the diet is high. In this study,
cows were allowed up to 18.1 kgjday of concentrate to allow
monitoring of both concentrate and silage intake; average
silage intake was 23.5 and 28.1% of DM intake for FC and for
SC, respectively.
Intake of NDF was 40.1 and 41.1% for C and BCF, 39.3
and 42.4% for HSP and LSP, 43.2 and 38% of total DM intake
for SC and FC cows, respectively; ideal NDF intake for
maximum DM intake and solids-corrected milk yield may be
39.1 + 1.8% of DM intake (12).
NEL intake was 7.9% higher with BCF than with C.
Calculated intake of rumen escape protein (REP) was 60%
higher with LSP than with HSP. Estimated microbial CP (MCP)
production was higher with BCF than with C. Intake of fiber
components were not affected by fat, however intake of ADF
was lower (P<.05) in fall calving cows and intake of

---

100
hemicellulose was higher (P<.OS) in cows fed LSP. Body
weight gain was lower (P<.OS) in cows fed
BCF or LSP and in
sc cows.
Effect of level of fat by level of REP treatment
combinations on intake of DM, concentrate and silage are
shown in table S and figure 2. Cows fed C and LSP tended to
consume more DM, concentrate and silage than other cows.
Intake of REP was higher in cows fed BCF and LSP than in
cows fed C and HSP or BCF and HSP. Intake of NDF was lower
in cows fed BCF and HSP than in cows fed C and LSP, or BCF
and LSP.
Digestibility data are reported in tables 6 for main
effects. Feeding fat increased digestibility of dry matter
and fiber components; the reason for the increase in fiber
digestibility is unclear. Digestibility of NDF and
hemicellulose was higher with LSP than with HSP.
Digestibility of fiber components usually decreases in sheep
with the addition of fat (33); however, Palmquist (20)
suggested that this is not necessarily true in lactating
cows; palmquist and Conrad (21) found that digestibility of
fiber was not affected by the addition of unprotected
lipids.
Effect of level of fat by level of REP treatment
combination are in table 7. Digestibility of DM tended to be
highest with cows fed BCF and LSP and lowest with cows fed C
and HSP; digestibility of CP tended to be highest with cows
fed BCF and HSP and lowest with cows fed C and HSP.

---

101
Milk production data are reported in table 8 for main
effects. positive numeric increases of 100 kg, 168 kg and
190 kg due to effect of fat, protein solubility and calving
season respectively, were observed in total milk production
(based on 16 wk). Peak milk yield occurred in wk 5 for BeF
and for LSP, in wk la for e and in wk 7 for HSP. In a 15-wk
study by Smith et al (28), a, 7 and 15% protected tallow was
fed and maximum milk yield occurred in wk 5 to 7 on aIl
diets, regardless of level of fat. Overall milk yield, and
milk yield at peak lactation were not affected by level of
fat or by level of REP. The lack of a significant response
in cows fed fat or REP may be an indication that there is
not much benefit to be expected from the addition of fat or
REP at the high concentrate intakes in the present study.
Effect of calving season on milk yield and average
daily temperature by lactation week are shown in figure 3.
There was no difference in total milk production, however Fe
cows produced significantly more (P<.05) milk than SC cows
during weeks 4, 5 and 6. Peak milk yield was reached during
week la for sc cows and during week 6 for Fe COWSi the time
lapse between peak lactation and peak dry matter intake was
5 and 4 weeks for sc and for Fe cows, respectively.
Temperature data (figure 4) indicates that average daily
temperature during peak milk yield was 15.8 and 11.2 Oc for
sc and Fe cows, respectively. Peak milk yield was 40.99 kg/d
for sc cows and 44.14 kg/d for Fe cows.

---

102
Fall calving cows produced more milk solids, fat, 5NF,
CP and lactose than summer calving cows. These results are
consistent with findings by Moody et al (13). Milk
composition was not affected by dietary fat or by protein
solubility.
Effect of treatment combinations on milk yield are
shown in figure 3. Milk yield, concentration of milk solids,
fat and 5NF tended to be highest for cows fed C and LSP
(table 9); This may be due to intake of DM, concentrate and
silage slightly higher than cows in the other groups. Milk
fat concentrations were low in aIl groups. High concentrate-
low roughage diets are known to lower milk fat concentration
(33). There was no effect of level of fat or prote in
solubility on milk protein content, or on efficiency of milk
protein production.
Estimated intake of metabolizable protein (MP), milk
protein yield and body weight (BW) changes are shown on
figure 5 for treatment combination effects. It appears that
cows consuming BCF+LSP tended to consume more MP and produce
more milk protein than other groups; cows fed C+H5P tended
to consume the lowest amount of MP. Cows fed C+H5P produced
slightly lower yields of milk protein than other groups.
Cows fed BCF+LSP lost more weight than other groups.
Cows fed C+LSP may have used nutrients more efficiently
since they tended to produce more milk than other groups
(figure 3), and started gaining weight sooner (figure 5).

---

103
Absorbable protein requirements are 3.1 and 3.6 kg/day
for mature lactating cows producing 30 kg/d of 4% fat
corrected milk and weighing 600 and 650 kg respectively
(16). Cows in this study weighed 617, 664, 648, 626 kg at
the end of the study, consumed 3.6, 3.9, 3.7 and 4.4 kg/d of
MP and produced 28.3, 31.2, 29.6, 30.1 kg/d of 3.5% FCM for
C+HSP, C+LSP, BCF+HSP, and BCF+LSP, respectively. MP intake
may have been higher than required in aIl groups, therefore
masking the effects of added REP.
MCP values listed in this study have been estimated
based on NEL content of feeds consumedi this allows NEL of
fat to artificially inflate MCP yield of fat-containing
diets since LCFA do not directly contribute to growth and
synthesis of MCP by rumen microbes. Furthermore the
prediction equation used for estimating MCP allows for
considerable error (16) and actual MCP yield of diets may
have been lower than values reported here.
Summer calving in warmer climates has economically
important negative effects on milk compositioni decreased
milk protein content due to fat may not be a problem at high
concentrate intake or with adequate intake of MP.
In this
study, dietary fat and REP did not significantly improve
production, however, these ingredients may be of more
benefit during early lactation or with high producing cows
when silage intake is maximized.

---

104
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1.
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2.
Annexstad, R.J., M.D. Stern, D.E. Otterby, J.G. Linn,
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gluten Meal as supplemented protein sources for
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3.
Banks, W., J.L. Clapperton, M. E. Ferrie, and A. G.
Wilson. 1976. Effect of feeding fat to dairy cows
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4.
Beede, D.K., and R.J. Collier. 1986. Potential
nutritional strategies for intensively managed cattle
during thermal stress. J. Anim. Sei. 62:543.
5.
Bines, J.A., P.E. Brumby, J.E. Storry, R.J. Fulford
and J.D. Braithwaithe. 1978. The effect of protected
lipids on nutrient intakes, blood and rumen
Metabolites and milk secretion in dairy cows during
early lactation. J. Agric. Sei. 91:135.
6.
Chandler, P.T. 1987. Problems of heat stress in dairy
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7.
Dunkley, W.L., N.E. Smith, and A.A. Franke. 1977.
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8.
Emery, R.S. 1978. Feeding for increased milk proteine
J. Dairy Sei. 61:825.

---

105
9.
Goering, H.K. and P.J. Van Soest. 1970. Forage fiber
analyses (apparatus, reagents, procedures, and some
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10.
Kirkpatrick B.K., and J.J. Kennelly, 1987. In situ
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Il.
MacLeod, G.K., Y. Yu, and L.R. Schaeffer. 1977.
Feeding value of protected animal tallow for high
yielding dairy cows. J. Dairy Sei. 60:726.
12.
Mertens, D.R. 1985. Factors influencing feed intake in
lactating cows: from theory to application using
neutral detergent fiber. Pages 1-18 in Proc. Ga. Nutr.
Conf. for the Feed Industry.
13.
Moody, E.G., P.J. Van Soest, R.E. McDowel1 and G.L.
Ford. 1968. Effects of high temperature and dietary
fat on performance of lactating cows. J. Dairy Sei.
50:1909.
14.
National Research Council. 1978. Nutrient Requirements
of Dairy Cattle. 5th revised ed. Natl. Acad. Sei.,
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15.
National Research Council. 1981. Effect of
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domestic animaIs. Natl. Acad. Sei., Washington, D.C.
16.
National Research Council. 1988. Nutrient Requirements
of Dairy Cattle. 5th revised ed. Natl. Acad. Sei.,
Washington, D.C.

---

106
17.
Nishimuta, D. G. Ely and J. A. Boling. 1974. RuminaI
bypass of Dietary Soybean prote in treated with heat,
formalin and tannic acid. J. Anim. Sci. 39: 952.
18.
~rskov, E.R., and I. Mc Donald.1979. The estimation of
protein degradability in the rumen from incubation
measurements weighted according to rate of passage. J.
Agric. Sci.
(Camb.). 92:499.
19.
~rskov, E.R., D.A. Grubb and R.N.B. Kay. 1977. Effects
of postruminal glucose or prote in supplementation on
milk yield and composition in Friesan cows in early
lactation and negative energy balance. Br. J. Nutr.
38:397.
20.
Palmquist, D.L. 1984. Use of fats in diets for
lactating dairy cows. p. 357-381. In J. Wiseman (ed.)
Fats in Animal Nutrition. Butterworths, London.
21.
Palmquist, D.L., and H.R. Conrad. 1978. High fat
rations for dairy cows. Effects on feed intake, milk
and fat production, and plasma Metabolites. J. Dairy
Sci. 61: 890.
22.
Palmquist, D.L. and E.A. Moser. 1981. Dietary fat
effects on blood insulin, glucose utilization, and
milk protein content of lactating cows. J. Dairy Sci.
64:1664.
23.
Robertson, J.B. and P.J. Van Soest. 1981. The
detergent system of analysis and its application to
human foods. p. 123. In: W.P.T. James and O. Theander

---

107
Ced.) The analysis of dietary fiber. Marcell Dekker,
New York, NY.
24.
SAS. 1982. SAS user's guide. Statistical Analysis
System Institute, Inc. Cary, N.C.
25.
Sahlu, T., D.J. Schingoethe, and A.K. Clarke. 1984.
Lactational and chemical evaluation of soybean meals
heat-treated by two methods. J. Dairy Sei. 67:1725.
26.
Sharma, H. R., J. Ingalls, J.A. McKirdy. 1978. Effects
of feeding protected tallow to dairy cows in early
lactation. J. Dairy Sei. 61:747.
27.
Schwab, C.G. and L.D. Satter. 1973. Response of
lactating dairy cows to the abomasal infusion of amine
acids. J. Dairy Sei 56:664.
28.
Smith, N. E., W.L. Dunkley, and A.A. Franke.1978.
Effects of feeding protected tallow to dairy cows in
early lactation. J Dairy Sei. 61:747.
29.
Spires, H.R., J.H. Clark, R.G. Derrig and C.L. Davis.
1975. Milk production response and nitrogen
utilization in response to postruminal infusion of
sodium caseinate in lactating cows. J. Nutr. 105:1111.
30.
Steel and Torrie. Principles and procedures of
statistics. 2nd ed. McGraw-Hill Book Company, Inc. New
York.
31.
Storry, J.E., P.E. Brumby, A.J. Hall, and V. W.
Johnson. 1974. Response of the lactating cow to
different methods of incorporating case in and coconut
oil in the diet. J. Dairy Sei. 57:61.

---

108
32.
Tilley, J. M. and R. A. Terry. 1963. A two-stage
technique for the in vitro digestion of forage crops.
J. Brit. Grassl. Soc. 18:104.
33.
Van Soest, P. J. 1963. Ruminant fat metabolism with
particular reference to factors affecting low milk fat
and feed efficiency. A review. J. Dairy Sei. 46:204.

---

109
FOOTNOTES
1American Calan, Inc. P. o. Box 307, Jenness Pond Rd.
Northwood, NH 03261.
2Boumatic Dairy Equipment Co. A division of D.E.C., Inc.
3Specifications for the Technicon Autoanalyzer II
Continuous-flow Analytical Instrument (Technical
Publication No. TSO-0170-2). 1975. Technicon
Instruments Corp. Tarrytown, NY
4Labconco Freeze Dryer Model 75040. Kansas City, MO.

---

Table 1. Characteristics of cows selected for the trial.
BLOCK
ITEM
1
2
3
4
SE
Milk yield (kg):
summer calving
8872
9127
9205
9118
596.9
fall calving
9666
9422
9333
9385
225.6
mean
9269
9275
9269
9252
171.1
Lactation number:
summer calving
4.7
4.0
2.3
2.3
.9
fall calving
2.7
3.0
3.0
3.3
.3
mean
3.7
3.5
2.7
2.8
.3
....
....
o

---

Table 2. Ingredient and partial eompositional analyses of dietary
eomponents (% of DM).
Coneentrate
Protein Ssupplement
Item
Control (C)
C+FAT
SBM
MIX
Silage
Corn
40.5
27.4
---
16.2
Soyhulls
30.4
29.6
Corn gluten feed
27.0
26.4
SBM
2.4
100.0
Toasted SBMa
50.0
Corn gluten meal
33.8
Blended fat
12.1
Dieal
.7
.7
Limestone
1.4
1.3
Component
Dry matter
91.6
91. 5
89.5
93.7
28.8
Crude protein
13.7
14.4
45.8
46.0
9.4
NDF
37.5
34.4
11.6
28.7
60.2
ADF
19.0
15.2
5.1
4.0
34.2
Cellulose
18.5
19.2
6.5
24.7
26.0
Hemieellulose
19.8
19.2
6.5
24.8
25.9
Lignin
1.0
1.1
.8
.7
5.2
Ether extraet
5.0
16.3
4.8
5.3
2.5
Ash
6.4
6.0
5.0
7.9
5.6
NEL (Meal/kg)
1.9
2.3
1.9
1.9
1.4
aSolvent extraeted SBM heated at 149 oC for 4 h.
....
....
....

---

Table 3. In situ disappearance and effective degradability of DM and
CP from dietary components.
Dietarv ComDonent
ITEM
Concentrate
HSpa
LSpa
Silage
SE
-------------------%--------------------
Disappearance:
41.2 b
31. 6d
DM
54.5c
36.4 e
1. 30
CP
53.1b
53.9b
19.2 c
73.8d
2.00
Degradabilityf:
38.6~
48.0gh
DM
51.2g
57.0g
2.70
CP
61.2i
64.6i
25.1)
75.8 k
8.20
aHSP gh solubility protein; LSP: low solubility proteine
bcdeMeans in the same row without a common superscript
differ (P<.OOOl).
fEffective degradability calculated as described by ~rskov and
McDonald (1979).
ghMeans in the same row without a common superscript differ
.·iP<.05).
1)
Means in the same row without a common superscript differ
(P<.Ol).
....
....
lU

---

Table 4. Nutrient intake and body veight changes of lactating dairy covs as
affected by level of fat, protein solubility and calving season.
Level Qf Fat
Prote in sourc>
Calving Season
Itell
o
1 kg/d
HSpa
LS
Sumaer
FaU
SE
Intake:
-------------------------kg
d.-------------------------
Dry lIatter
20.2
19.0
19.6
19.6
19.2
20.0
.50
Silage
5.3
4.9
5.0
5.1
5.4
4~7
.29
Crude Prote!n
3.4
3.4
3.4
3.5
3.3
3.5
.07
Escape Prote!n
1.4
1.4
1.2 c
1.6d
1.7
1.8
.06
NDF
8.1
7.8
7.7
8.3
8.3
7.6
.93
ADF
3.9
3.6
3.7
).8
4.0 c
3.5d
.52
Hellicellulose
4.3
4.2
4.0c
4.5d
4.3
4.1
.46
Cellulose
3.0
2.8
2.8
3.0
3.2
2.6
.48
-------------------------Hcal/kg-----------------------
NELe
36.8c
39.0d
37.3
38.5
38.1
37.8
.55
---------------------------\\---------------------------
DH, \\
BW f
3.3c
3.)c
3.)c
3.3c
3.4 c
3.2 c
.30
;;~;~-------~;d-----;;~:~/d o~ ~~~d----=-;~~~-----;;~;d
Weight gain
8.90
Body veightg
641
637
63)
645
621
657
I l . 90
HCpl'I
2.4 c
2.6d
2.5
2.6
2.5
2.5
.02
abHSp : high solubility protein: LSP: lov solubility protein.
cdHeans vith the salle superscript are not different (P<.05).
eCalculated based on NEL content of dietary cOllponents (NRC, 1978).
f DH intake(kg)/body veight.
9Body veight after 16 veeks.
hHicrobial crude protein calculated based on NEL intake (NRC, 1985).
....
....
w

---

Table 5. Nutrient intake and body weight of lactating dairy cows as
affected by treatment combinations.
Treatment Combinationa
Item
C.H5P
C.LSP
BCF.HSP
BCF.LSP
P
Intake (DM):
---------------kg/d----------------
Dry matter
20.0
20.5
19.3
19.6
NSb
Silage
5.1
5.4
4.9
4.8
NS
CP
3.3
3.5
3.4
3.5
NS
Escape protein
1.2c
1.4cd
1.2c
1.7d
.01
NDF
8.0cd
8.3 c
7.4 d
8.2 cd
.08
ADF
3.8
3.9
3.6
3.7
NS
Hemicellulose
4.2 cd
4.4 d
3.8c
4.6d
.02
Cellulose
3.0
3.0
2.7
2.9
NS
--------------Mcal/d---------------
NEL
36.7c
37.0c
38.0cd
40.0d
.06
----------------kg-----------------
Body weighte
617
664
648
626
NS
Weight gain
39.0c
20.6c
26.5c
-24.6d
.01
MCpf
2.4 c
2.5c
2.5c d
2.7d
NS
aC: control; BCF: control plus 1kg/d fat; HSP: high solubility
protein; LSP: low solubility proteine
bNot significant at P<.05.
cdMeans in the same row without a common superscript differ.
eBody weight after 16 wk.
fMicrobial CP calculated using NEL values, as indicated by NRC
(1988).
~
~
~

---

Table 6. Nutrient digestibility by lactating dairy cows as affected by level
of fat, protein solubility and calving season.
Level of Fat
Prote in Source
Calving Season
Item
o
1 kg/d
HSpa
LSpa
Summer
Fall
SE
--------------------------\\---------------------------
Dry matter
68.0b
70.1c
70.3
68.4
68.4
70.3
.55
CP
57.4 b
64.5 c
64.1b
57.9c
58.3
63.6
1.47
NDF
55.2b
59.3c
56.5
57.7
57.3
56.9
.67
ADF
54.1
56.5
55.8
54.8
55.6
54.9
.69
Hemicellulose
55.3 b
61.3 c
56.7
59.9
58.6
58.0
.90
Cellulose
49.3 b
54.9 c
51.1
53.1
53.7
50.5
1.06
aHSP: high solubility proteini LSP: low solubility proteine
bCMeans in the same row without a common superscript differ (P<.05).
....
....
11l

---

Table 7. Nutrient digestibility by lactating dairy cows as affected
by level of fat by protein solubility treatment
combinations.
Treatment Combinationa
Item
C.HSP
C.LSP
BCF.HSP
BCF.LSP
P
----------------%-----------------
Dry matter
69.0bc
66.9b
71.5c
69.9bc
.01
CP
6l.3 bc
53.4 b
66.6c
62.3 c
.05
NDF
54.5b
55.9bc
58.6dc
59.4 d
.05
ADF
53.8bc
54.3 b
57.7bc
55.3 c
.07
Hemicellulose
55.lb
55.6b
58.3 b
64.2 c
.05
Cellulose
48.9b
49.7 b
53.3 bc
56.5c
.05
aC: control; BCF: control plus 1kg/d fat; HSP: high solubility
protein; LSP: low solubility proteine
bcdMeans in the same row without a common superscript differ.
....
....
0\\

---

Table 8. Average milk yield and composition of milk from lactating cows as
affected by level of fat, protein solubility and calving season.
Level of Fat
Protein Source
Calvinq Season
Item
o
1 kg/d
HSpa
LSpa
Summer
Fall
SE
--------------------------%----------------------------
Solids
11.4
11.3
11.1
11.6
11.0b
11.7c
.13
Fat
2.5
2.4
2.4
2.5
2.3 b
2.6 c
.08
SNF
8.9
8.9
8.8
9.0
8.7b
9.1 c
.08
CP
3.3
3.4
3.3
3.3
3.2 b
3.4 c
.05
Lactose
4.9
4.9
4.7
5.0
4.8
5.0
.06
MineraIs
.7
.7
.7
.7
.7
.7
.01
--------------------------kg/d.------------------------
Milk
38.9
39.8
38.6
40.1
38.5
40.2
.70
Fat
1. 0
• 9
. 9
1. 0
• 9b
1. OC
.04
SNF
3.4
3.5
3.4
3.6
3.3b
3.6c
.07
CP
1.3
1.3
1.3
1.3
1.2b
1.4c
.04
Lactose
1.9
1.9
1.8b
2.0c
1.8b
2.0 c
.04
MPPId
. 4
• 4
. 4
• 4
. Sb
. 4c
.01
aHSP: high solubility protein; LSP: low solubility proteine
bCMeans in the same row without a common superscript differ (P<.05).
dMilk CP (kg)/ CP intake (kg).
....
1-'
.....,

---

Table 9. Average yield and composition of milk from lactating
dairy cows as affected by treatment combinat ion
Treatment Combinationa
Item
C.HSP
C.LSP
F.HSP
BCF.LSP
P
----------------,-----------------
Solids
11.0b
11.7c
11.2bc
11.4 bc
.02
Fatd
2.4 bc
2.7c
2.4 b
2.4 bc
.05
SNF
a.a b
9.1c
9.0bc
9.1bc
.05
CP
3.2
3.3
3.4
3.3
NS e
Lactose
4.7
5.0
4.7
5.0
NS
MineraIs
.7
.7
.7
.7
NS
----------------kg/d--------------
Milk
37.53
40.29
39.62
39.93
NS
Fat
.9b
1.lc
.9bc
.9b
.04
SNF
3.2b
3.6c
3.5bc
3.5bc
.03
CP
1.2
1.3
1.3
1.3
NS
Lactose
1.ab
2.0c
1.9bc
1.9bc
.01
MPPI f
.4
.4
.4
.4
NS
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---

EFFECT OF DIETARY FAT ON L-LYSINE, L-PHENYLALANINE, L-LEUCINE
AND L-METHIONINE UPTAKE BY BOVINE MAMMARY TISSUE IN VITR01.
1Nianogo, A. J., H. E. Amos, M. A. Froetschel, R. Dean
and J. M. Fernandez. To be submitted to Journal of Dairy Science.
129

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130
ABSTRACT
Four mature lactating cows were blocked into two
groups based on milk production to determine the effect of
dietary fat on amino acid (AA) uptake by mammary tissue. The
study was conducted as a replicated reversaI with two 21-day
periods and 2 dietary treatments. Dietary treatments were :
A) control diet, and B) A plus 1 kg/day blended animal and
vegetable fat. Cows were fed sorghum (Sorghum bicolor L.)
silage ad libitum. Blood samples were collected from the
jugular vein on day 15, 17 and 19 of each periode At the end
of the second period cows were slaughtered and mammary
tissue sampled for incubation in Krebs Ringer bicarbonate
buffer containing aIl 22 AA'a at physiological arterial
concentration and .225 ~ci/ml of 14C-Iabelled L-Leucine, L-
Phenylalanine, L-Lysine or D/L Methionine. Dry matter
intake, milk yield and milk composition were not affected by
fat addition. Yield of milk CP was 18.9% lower, plasma total
lipids increased 33.6% and plasma glucose decreased 9.0% in
cows fed 1 kg/day fat. Dietary fat decreased mammary tissue
slice uptake of AA by 21.21%. Uptake was 4.8, 10.3, 17.8 and
2.4 x 10-3 ~M/min/gm of tissue dry matter for phenylalanine,
lysine, leucine and methionine, respectively. Level of
insulin did not affect AA uptake. Results suggest that
dietary fat may decrease milk prote in synthesis by lowering
the rate of AA uptake in mammary tissue.
,KEY WORDS: dietary fat, amino acid uptake, bovine, mammary
tissue.

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131
INTRODUCTION
The inclusion of fat in diets for lactating cows has
frequently resulted in subnormal milk protein concentration
(1, 3, 5, 9, 16, 18, 23) or yield (3, 5, 8, 16). Whether
this results from insufficient flow of metabolizable protein
from the rumen or from some effect of dietary LCFA on
mammary tissue metabolism is unclear at the present time.
Dunkley et al (8) have reported a decrease in microbial
protein synthesis in cows fed fat, and Nianogo and Amos
(unpublished)
found that efficiency of milk protein
production may increase in cows fed fat and rumen escape
proteins. Palmquist and Moser (18) reported a decrease in
plasma insulin level in one experiment and a decreased
tissue sensitivity to insulin of cows fed high levels of fat
in another.
Short-acting insulin injections into lactating cows
have decreased milk yield but increased milk protein
concentration (22). Cummins and Russell (6) found that in
vitro uptake of palmitate and glucose by mammary tissue was
decreased by dietary fat. The effect of dietary fat on
mammary tissue uptake and metabolism of amine acids has not
been investigated to date. Pocius and Baumrucker (19) have
developed a method for measuring bovine mammary amine acid
uptake in vitro. Amino acid transport systems in bovine
mammary tissue have been reviewed recently (4).
The objectives of this study were to determine if:
1) amine acid uptake is altered in cows fed 1 kg fat daily;

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132
2) the rate of uptake is similarly affected for amino acids
that are transported by different systems; 3) the effect of
insulin level on amino acid uptake.
MATERIALS AND HETHODS
Production trial: Four mature lactating cows were
blocked into 2 groups based on milk production; cows were
randomly assigned to one of 2 dietary treatments in a
replicated reversaI which included two 21-day periods, 2
dietary treatments and the 2 groups of cows. Dietary
treatments were : A) control diet, balanced to meet NRC
recommendations for maintenance and production; B) A plus 1
kg/day blended animal and vegetable fat substituted for
corn. Lipid supplement was yellow grease and included 44.9%
C18:1, 21.4% C16:0, 12.3% C18:0, 10.2% C18:2, 3.5% C16:1,
1.8% C14:0, 1.6% C18:3 and less than 1% of C14:1, C16:2 and
C17:0, and was fed for a maximum intake of 1 kg/day. Cows
were trained to use CALAN gates for about 1 week and were
allowed 2 weeks for dietary adjustment. Cows were fed their
concentrate diets using a BOUMATIC computerized feeder with
2 feeding stations. Sorghum silage was fed ad libitum
through CALAN gates.
Sodium bicarbonate note and a trace
mineraI mix were provided ad libitum.
Diet and orts were sampled daily, cows were milked
twice daily and milk was sampled during each milking on day
15 through 21. Cows were also weighed on day 19, 20 and 21.
Blood samples were collected on day 15, 17 and 19 at 0800,

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133
1400 and 2000 h from the jugular vein, into centrifuge tubes
containing 2 drops of heparin.
Diets and orts were dried at 60 0 C for 72 h, ground
through a 1 mm Wiley mill screen and composited. These
samples were subsequently analyzed for ether extract by
soxhlet, gross energy and ash (2) and for NDF, ADF,
cellulose and lignin as described by (20). Crude protein was
determined on a Technicon Model II Autoanalyzer after
digestion on a block digester.
Total milk solids were determined in duplicate in 10
ml of milk lyophilized in Gooch crucibles on a Labconco
model 75040 freeze dryer. Milk fat was determined by the
Babcock method (2) and milk protein was determined as
described.
Blood samples were placed in ice, and plasma was
separated by centrifugation at 8000 x 9 for 15 min. Plasma
samples were kept frozen until analyzed. Plasma
immunoreactive glucagon was assayed as described by (12).
Rabbit anti-porcine glucagon antibody (Unger 04A, Pool1, Lot
12) specifie for small molecular weight (3,500 M.W.)
glucagon was used at a final dilution of 1/225,000. Purified
bovine-porcine standard (Sigma Chemical Company, st. Louis,
MO) was the source of standard. Porcine I-Glucagon
(Cambridge Medical Diagnostics, Inc., Billerica, MD) was the
radioligand, and goat anti-rabbit immunoglobulin G (Research
Products International Corp., Mt. Prospect, IL) was used at
a 1/60 dilution as the precipitating antibody. AlI samples

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134
were assayed in duplicate. Intraassay coefficient of
variation as determined by pooled bovine plasma samples was
4.9%.
Plasma immunoreactive insulin was assayed as described
by Kopowski and Tucker (14). Guinea pig anti-bovine insulin
antibody (ICN ImmunoBiologicals, Lisle, IL) was used at a
final dilution of 1/60,000, while purified bovine insulin
(26.6 ~U/ng, Lilly Research Laboratories, Indianapolis, IN)
and bovine 125I -insulin (Amersham Corporation, Arlington
Heights, IL) were used as the standard and radioligand,
respectively. Goat anti-guinea pig immunoglobulin G (Sigma
Chemicals Co., st. Louis, MO) was used at a 1/16 dilution as
the precipitating antibody. The intraassay coefficient of
variation as determined by pooled bovine and caprine plasma
samples was 3.7%. Plasma glucose was determined on a YSI
Model 27 Industrial Analyzer, and total lipids were
determined as described by Folch et al (10).
statistical analyses were performed using SAS (1982)
general linear models. The main effects were level of fat
and period for intake, milk production, plasma components
and body weight data.
Treatment means were separated by the t test.
Tissue incubation: The incubation study was designed
as a 2 x 3 x 4 x 5 factorial, with 2 replications per celle
Factors included were: 2 levels of dietary fat (0 and
1kg/day), 3 incubation times (30, 60 and 120 min), 4 AA:
lysine, leucine, phenylalanine and methionine (AA were

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135
obtained from USB) , and 5 levels of insulin (0,
.1, .2, .4
and .8 lU/ml).
Incubation media was modified Krebs-Ringer bicarbonate
(KRB) buffer ; KRB buffer (pH 7.4) contained 118 mM sodium
chloride, 4.74 mM potassium chloride, 2.54 mM calcium
chloride, 1.18 mM potassium phosphate (monobasic), 1.18 mM
magnesium sulfate, 24.9 sodium bicarbonate, 10 mM acetate,
10 mM glucose, as described by Pocius and Baumrucker (19).
Amino acids listed by (15) were included in the media at
concentrations approximating arterial bovine blood.
At the end of the second period of the production
trial, cows were transported to the University of Georgia
abattoir and slaughtered.
Mammary tissue was removed within
3 min of kill and approximately 500 gm of tissue was excised
and submerged into ice-cold KRB buffer. Tissue was sliced
using a Stadie-Riggs microtome (Thomas, Philadelphia, PA),
blotted on kimwipe paper and weighed; slices weighing 200 to
400 mg were selected for incubation. Remaining tissue parts
were frozen for later analysis. Weighed slices were placed
in glass scintillation vials pre-gassed with 95:5 02:C02
containing 5 ml of modified KRB buffer, a mixture of aIl 22
AA at physiological concentrations, and .225 ~Ci/ml of L-[U-
14C] lysine, L-[U_14C] leucine, L-[U_14C] phenylalanine, or
L-[CH3-14C] methionine. 14c labelled AA were obtained from
ICN Biochemicals. Scintillation vials were again gassed with
02:C02 for 30 sec then placed in a Lab-Line/CS & E Imperial

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136
II incubator. Samples were allowed to equilibrate for 15 min
at 37° Cprior to actual incubation.
After incubation, vials were placed in a freezer for
30 min to stop tissue activity. Incubation media was
subsequently discarded and vial and remaining tissue were
rinsed 4 times with distilled water. Tissue samples were
then solubilized in the vials with 1 ml Beckman tissue
solubilizer-450. Following tissue solubilization, 2 drops of
30% hydrogen peroxide were added to each flask. Ten ml
Beckman liquid scintillation cocktail Ready-Solv HP/b was
also added and scintillation vials were placed in a HEWLET
PACKARD scintillation counter to measure 14C activity.
Samples of stock solutions of 14C labelled AA were also
counted to measure initial activity. Total AA in culture
media was estimated as: TAAm = AA + AA* where TAAm was the
total AA of a given kind in the media, AA is the quantity of
that AA in the KRB buffer, and AA* is the amount of 14C-
labelled AA. Specifie activity was computed as: DPM added as
AA* / TAAm; AA uptake (U) was measured as:
U (mg/gm or J.'M/gm DM) = AAt (mg or J.'M)/DMt (gm),or
U (mg/gm or J.'M/gm CP) = AAt (mg or J.'M)/CPt (gm); where AAt
is the total amount of AA found in the tissue, DMt is the
dry weight of the tissue and cPt the total CP content of the
tissue.
Tissue samples were analyzed for DM, CP and total
lipids as described.
For in vitro data the model was:

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137
Yijklm = ~ + Fi + Ij + Tk + Al + cm(Fi) + F*I + F*T + F*A +
I*T +
I*A + T*A + F*I*T + F*I*A + F*T*A +
I*T*A + F*I*T*A + F*I*T*A*C + Eijklm;
where Yijklm is the variable of interest, F is the level of
fat, l is the level of insulin, T is the time, A is the
amino acid type and C is the cow (nested within level of
fat). Non-significant 3 and 4 way interactions (P>.10) were
subsequently included in the residual error terme
Statistical analysis of the data was performed, using SAS
general linear model. Treatment means were compared 2 at a
time using the t test (25).
RESULTS AND DISCUSSIONS
Pretrial milk production was 15.65 kg/d for block 1
and 14.29 k9/d for block 2. Ingredient composition and
partial compositional analyses of diets are shown in table
1. Adding 12.1% fat to the concentrate provided 20.7% more
NEL. Dry matter intake (DMI), body weight and milk
production data are in table 2. Milk yield declined 16%
while milk fat content increased 15.2% with fat addition;
yield of milk SNF, crude prote in and lactose were 18.2, 20
and 20% lower respectively in cows fed 1 kg/day fat (table
2) •
Dietary fat increased (P<.OOOl) plasma total lipids
and glucagon and decreased (P<.OOOl) plasma glucose (table
3).
The increase in plasma lipids is consistent with

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138
findings by (11, 16, 24); lipids increasing with dietary fat
intake include plasma NEFA, triglycerides and cholesterol
(24). Plasma glucose level fluctuates with dietary fat,
depending on source of fat and source of carbohydrate in
diet. In one study, Palmquist and Moser (18) observed
numeric increases of 10.95 to 17.94% with the addition of
fat; in another trial (18), glucose level decreased 4.0%.
Dietary fat increased plasma glucagon 29.2% (P<.OOl)
but plasma insulin level was not affected. This caused the
insulin: glucagon ratio (IGR) to be lower in fat fed cows
(P<.OOOl). Insulin levels have decreased or remained the
same in other studies (18). It is not clear why dietary fat
would cause plasma glucagon to be elevated; however,
decreased insulin would create conditions similar to
increased glucagon, due to the antagonism between these two
hormones.
Both insulin and glucagon stimulate the uptake of most
unbranched neutral amine acids in isolated rat hepatocytes,
by initiating a series of reactions which proceed without
the presence of free hormone (13). The IGR may be important
for protein synthesis since insulin can reverse AA transport
which had been enhanced in vivo by exogenous glucagon or by
induced diabetes; at excessive doses however, the
stimulatory effect of insulin was found to be additive to
that of glucagon in perfused rat liver. Further research is
needed to assess the exact role of insulin and glucagon in
AA uptake and metabolism in the mammary gland.

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139
Uptake of amine acids (~M/min/gm of tissue DM) by
mammary tissue slices was 21.21% lower (P<.OOOl) in cows fed
dietary fat (table 4).
Protein content did not appear to
affect these differences. Average uptake was 4.8, 10.3, 17.8
and 2.4 ~M/min/gm tissue DM for phe, lys, leu, and met,
respectively. Rate of uptake decreased (P<.OOOl) with time,
probably as a result of a decrease in tissue activity (table
5). Insulin had no effect on uptake. This contrasts with
findings with dairy cows (22) and observations with other
species (13). However, Kilberg (13) reported that insulin is
only required in the initial stages of amine acid uptake
into isolated rat hepatocytes; it is possible that tissue
freshly removed from the mammary gland had been sufficiently
exposed to insulin in vivo.
Higher uptake of lysine and leucine is consistent with
(19) and with findings that percentage extraction of AA is
not uniformly related to plasma concentration (4).
Baumrucker (4) indicated that bovine mammary tissue
possesses a sodium independent transport system for cationic
amino acids; this system is not sensitive to specifie
inhibitors of the neutral AAtransport systems and allows
excess uptake of cationic AA. Baumrucker (4) indicated that
Ile and Leu may be taken up in excess as weIl. Both Leu and
Met may be taken up by a system specifie for small
unbranched side chains, Met is taken up by the system for
neutral AA with small sidechains, Leu and Phe by a system
specifie for large branched sidechains.

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140
It has been previously suggested that feeding fat may
decrease glucose metabolism in mammary and adipose tissue of
lactating cows (24). Decreased fatty acid synthesis and
decreased glucose oxidation have been shown to occur in
adipose tissue of cows fed high fat diets (27). In this
study, mammary tissue of cows that were fed fat contained
less CP and less lipids (table J); feeding fat may cause a
depletion of mammary tissue due to decreased entry of
substrates. Cummins and Russell (6) found that feeding whole
cottonseed decreased uptake of glucose and palmitate in both
adipose tissue and mammary tissue and also decreased glucose
oxidation to carbon dioxide in both tissues. Our results
indicate that increasing insulin level does not affect in
vitro uptake of AA, regardless of level of fat. There may be
a more generalized negative effect o~ dietary fat on mammary
tissue metabolism of organic compounds than previously
thought.
Outside of the unresolved role of insulin and other
hormones in the lactating mammary tissue, it is not clear
how dietary fat would lower milk protein production. One
possibility is that the decreased production of acetate
often observed with high fat diets may limit the supply of a
readily available energy source to the mammary and to other
tissues. Synthetic processes require energy in the form of
ATP and it is known that acetate is the chief contributor in
the mammary gland (7). Furthermore, postruminal infusions of
acetate has been shown to increase milk lactose content and

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141
milk protein yield (21). Milk prote in concentration did not
increase (21) because the increase in lactose caused an
increase in fluid volume.
Emery (9) suggested that milk protein concentration
tends to increase with increased intake of concentrate and
decrease with increased intake of fiber: however, if
concentrate intake remains adequate, milk protein content
should not decrease as a result of high fiber intake.
storry et al (26) found that unprotected coconut oil
caused the acetate: propionate ratio and milk protein yield
to decline: protected coconut oil did not alter the acetate:
propionate ratio or milk protein yield. Milk prote in
concentration has decreased with unprotected fats: however
it is conceivable that at high milk output the rate of
prote in synthesis in the mammary gland may become limiting,
particularly if substrate entry and energy supply are
limiting.
In order to fully understand the interaction between
dietary fat and milk protein synthesis, there may be a need
to reassess the role of metabolic hormones including insulin
and glucagon, and the role of substrate and energy supply to
the lactating mammary gland.

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142
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1.
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Banks, W., J.L. Clapperton, M. E. Ferrie, and A. G.
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143
8.
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144
16.
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Palmquist, D.R. and E. A. Moser. 1981. Dietary fat
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Pocius,·P.A. and C. R. Baumrucker. 1980. Amino acid
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Robertson, J. B. and P.J. Van Soest. 1981. The
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22.
Schmidt, G. H. 1966. Effect of insulin on yield and
composition of milk of dairy cows. J. Dairy Sei.
49:381.

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145
23.
Sharma, H.R., J. Ingalls, J. A. McKirdy. 1978.
Replacing barley with protected tallow in the ration
of lactating Holstein cows. J. Dairy Sci. 61:574.
24.
Smith, N. E., W.L. Dunkley and A.A. Franke. 1978.
Effects of feeding protected tallow to dairy cows in
early lactation. J. Dairy Sci. 61:747.
25.
Steel, R.G.D., and J.H. Torrie, 1980. Principles and
procedures of statistics. 2nd ed. Mc Graw Hill Co.,
New York, NY.
26.
Storry, J.E., P.E. Brumby, A.J. Hall, and V.W.
Johnson. 1974. Response of the lactating cow to
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27.
Yang, Y.T., R.L. Baldwin and W.N. Garrett. 1960.
Effects of dietary lipid supplementation on adipose
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47:686.

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146
FOOTNOTES
1American Calan, Inc. P. o. Box 307, Jenness Pond Rd.
Northwood, NH 03261.
2Boumatic Dairy Equipment Co. A division of D.E.C., Inc.
3Spec ifications for the Technicon Autoanalyzer II
Continuous-flow Analytical Instrument (Technical
Publication No. TSO-0170-2). 1975. Technicon
Instruments Corp. Tarrytown, NY
4Labconco Freeze Dryer Model 75040. Kansas City, MO.
5Yellow Springs Instruments Co, Inc. Yellow Springs, OH.
6United States Biochemical Corp. Cleveland, OH 44128.
7chicago Surgical & Electrical Co., div. Lab-line
Instruments, Inc.
8Beckman Instruments, Inc., Fullerton, CA 92634.

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147
Table 1. Ingredient composition and partial
compositional analysis of diets.
Item
Control
1kg/day Fat
Silage
Corn
40.5
27.4
soyhulls
30.4
29.7
Corn gluten feed
27.0
26.4
SBM
2.4
Fat
12.1
Dical
.7
.7
Limestone
1.4
1.3
Dry matter
91.6
91.5
28.8
Crude prote in
17.1
18.0
11.7
NDF
37.5
34.4
60.2
ADF
19.0
15.2
34.2
Hemicellulose
19.8
19.2
25.9
Ether extract
5.0
16.3
2.5
Ash
6.4
6.0
5.6
NELa (Meal/kg)
1.9
2.3
1.4
aCalculated from NRC (16).

---

148
Table 2. Intake, body weight, milk yield and milk
composition from lactating dairy cows as
affected by level of dietary fata.
Item
0
1 kg/day
%change
SE
Intake, DM:
Silage
6.4
5.6
-12.5
.47
Dry matter
16.0
15.5
-3.1
.26
Milk components:
-------%-------
Solids
13.6
12.6
-7.4
.49
Fat
3.3
3.8
+15.2
.22
SNF
9.2
8.8
-4.4
.31
CP
4.5
4.3
-4.4
.14
Ash
.8
.8
0.0
.01
Lactose
4.0
3.7
-7.5
.35
Y'ield
----kg/day-----
Milk
11.9
10.0
-16.0
.36
Fat
.4
.4
0.0
.02
SNF
1.1
.9
-18.2
.04
CP
.5
.4
-20.0
.02
Lactose
.5
.4
-20.0
.03
-------kg------
Body weight
704
700
-.6
22.97
weight gainb
10.5
9.0
-14.3
6.38
aNo difference between means at P<.05.
bEnding body weight.

---

Table 3. Effect of dietary fat on mammary tissue composition and
on plasma insulin, glucagon, glucose and total lipids of
lactating Holstein cows.
Item
Na
0
1 kg/day
% Change
SE
Tissue (%):
Dry matter
4
19.6
23.4
-19.4
1. 30
Crude protein
4
60.2
53.9
-10.5
4.42
Total lipids
4
40.7
34.7
-14.7
4.20
Plasma:
Glucose (mg/dl)
72
67.6b
61.5c
- 9.0
.58
Total lipids (mg/dl)
72
497.7b
665.0c
+33.6
15.00
Insulin (~U/ml)
72
18.7
19.7
+ 5.4
.62
Glucagon (pg/ml)
72
126.9b
163.9c
+29.2
3.08
Insulin/glucagon (M/M)
72
3.3 b
2.6c
-21.2
.11
aNumber of observations.
bCMeans within the same row without a common superscript differ (P<.OOOl).
....
01:>-
\\0

---

Table 4. Effect of dietary fat and amino acid type on uptake of 4
selected amino acids by bovine mammary tissue slices in
vitro.
Leyel of Fat
Amino Acid
Uptake
o
1kg/day
Phe
Lys
Leu
Met
SE
-----------------------x 10-3 ------------------------
Per gm tissue DM:
~M
9.9a
7.Sb
4.Sc
10.3d
17.Se
2.4f
.36
mg
1.4a
1.lb
.Sc
1.Sd
2.3e
.4f
.OS
Per gm tissue CP:
~M
16.1a
14.9b
S.Sc
lS.ld
31. 3e
4.1f
.63
mg
2.3a
2.1b
1.4c
2.6d
4.1e
.6f
.OS
abcdefFor level of fat and for amino acid type, means in the same row
without a common superscript differ (P<.OOOl).
....
ln
o

---

151
Table 5. Effect of incubation time on rate of
amino acid uptake by bovine mammary
tissue slices in vitro.
Incubation Time (min)
Uptake
30
60
120
SE
J..'M/gm/min:
-------------x
3
10- --------------
in DM
13.5a
8.2b
4.7c
.36
in CP
23.7a
14.5b
8.3c
.63
abcMeans without a common superscript differ
(P<. 0001) .

---

CONCLUSIONS
Dietary fat may help increase the productivity of
high producing or early lactating dairy cows.
Milk yield
and milk fat often increase as a result of fat addition.
However, negative effects are also observed: decreased
intake of DM affecting intake of important nutrients;
decreased production of milk or milk fat due to low DM
intake or to low digestion of fiber.
Efficiency of milk
protein production is often reduced by fat.
Increasing protein intake may improve body condition
in cows receiving significant amounts of fat.
Increasing
intake of rumen escape prote in (REP) may contribute to
higher production, particularly in cows receiving high
levels of fiber.
Furthermore, efficiency of milk protein
production is higher with low-protein high REP diets.
Feeding dietary fat may inhibit some synthetic
processes in the mammary gland, by reducing the rate of
uptake of essential nutrients, including amino acids.
The
decreased milk protein often observed with high fat diets
may result from a change in plasma hormonal patterns, a
decrease in the uptake of essential substrates or both.
Our
studies showed that uptake of amino acids was reduced 21.2%
by the addition of fat. Although it is still not clear why
fat would inhibit active transport in the mammary gland, the
152

---

153
possibility exists that hormones or energy supply may be
involved. The supply of preformed long chain fatty acids is
increased while the supply of ruminaI acetate may decrease.
This in turn may affect plasma hormonal patterns or energy
balance in mammary tissues, eventually lowering the rate of
protein synthesis.

---