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J. Dairy Sci. 84:462–470
American Dairy Science Association, 2001.
Effect of Site and Source of Energy Supplementation
on Milk Yield in Dairy Cows
A. Arieli,* S. Abramson,* S. J. Mabjeesh,*
S. Zamwel,* and I. Bruckental†
*Faculty of Agricultural, Food and Environmental Sciences
Department of Animal Sciences, Rehovot 76100, Israel
†Institute of Animal Science, Agriculture Research Organization
The Volcani Center, Bet Dagan 50250, Israel
ABSTRACT
The effect of infusing similar energy equivalents of
starch into the rumen, or starch or oil into the aboma-
sum was studied in four midlactation cows in a 4 × 4
Latin square design experiment; controls were rumi-
nally infused with water. Cows were fitted with cannu-
las in the rumen, abomasum, and ileum, and nutrient
digestion in the rumen and small intestine was evalu-
ated with Cr as a digesta marker. Ruminal infusions
of starch, or abomasal infusions of starch or oil, were
associated with a decrease in voluntary feed organic
matter intake. Overall energy intake was reduced in oil-
infused, but not in starch-infused cows. Nonstructural
carbohydrate digestibility in therumen and in the small
intestine was similar among treatments. In abomasally
infused cows 3.4 kg/d of nonstructural carbohydrates
was apparently digested in the small intestine. Milk
production was reduced in oil-infused cows, but the
efficiency of milk energy and protein yield was unaf-
fected by treatments. Plasma glucose, insulin, and IGF-
1 concentration, mammary glucose extraction rate, ru-
men ammonia and plasma urea, and arterial and mam-
mary extraction rate of amino acids were all similar
among treatments. Large quantities of starch can be
digested in the rumen or small intestine of dairy cows.
There appear to be no metabolic advantage to increas-
ing the supply of starch to the rumen or the abomasum
of mid-lactation dairy cows maintained on highly con-
centrated diets and exhibiting a positive energy
balance.
(Key words: starch digestibility, small intestine,
milk yield)
Received May 25, 2000.
Accepted September 20, 2000.
Corresponding author: A. Arieli; e-mail: arieli@agri.huji.ac.il.
462
Abbreviation key: AS = abomasally infused starch,
CONT = control, EAA = essential AA, OIL = abomasally
infused corn oil; RS = ruminally infused starch.
INTRODUCTION
Genetic improvements have presented a physiologi-
cal challenge for animal nutritionists, as how to provide
the extra nutrients required for increased milk energy
output in high-yielding dairy cows. When feed intake
is limited, dietary energy concentration must be in-
creased to supply these animals’ metabolic needs. Theo-
retical considerations suggest that starch is better uti-
lized for gain by steers when it is digested in the small
intestine, compared with digestion in the rumen (Ow-
ens et al., 1986). On the other hand, there is some
evidence that the effect on milk yield of starch supple-
mentation to the rumen is higher than that of intestinal
starch supplementation (Theurer et al., 1999).
It has been suggested (Huntington, 1997) that the
primary reason for incomplete starch digestion in the
small intestine is due to a lack of adequate pancreatic
amylase activity. According to a recent review (Reyn-
olds et al., 1997), the highest reported amounts of starch
digested by dairy cows is 2.4 kg/d. This figure, obtained
in cows producing 18 kg/d of milk, is much lower than
reports of postruminal digestion of 4 to 5 kg of starch/
d in dairy cows maintained on high-concentrate diets
(McCarthy et al., 1989; Overton et al., 1995; Shabi et
al., 1999). While part of the apparent variation in the
estimated capacity of dairy cows to digest starch might
be related to digestion of rumen escape starch in the
large intestine (Orskov, 1986), an underestimation of
small intestinal starch digestibility in high-producing
dairy cows cannot be ruled out.
Besides affecting the efficiency of milk energy produc-
tion, greater energy intake increases both the content
and yield of milk protein (DePeters and Cant, 1992).
In some cases, increased starch digestion in the rumen,
achieved by steam-flaking sorghum or corn grains, was
associated with increases in milk protein concentration
SITE AND SOURCE OF ENERGY SUPPLEMENTATION 463
or yield (Theurer et al., 1999), which could be explained
by improved microbial protein synthesis in the rumen.
In dairy cows maintained under a hyperinsulinemic-
euglycemic clamp, milk protein yield was increased by
insulin and by abomasal infused casein (Griinari et al.,
1997). This latter experiment demonstrated that the
milk production potential of dairy cows is not com-
pletely used, and that, besides supplying nutrients, di-
etary components also play key roles in controlling the
expression of the signals that regulate metabolic pro-
cesses. On the other hand, with the hyperinsulinemic-
euglycemic clamp (Griinari et al., 1997), milk protein
efficiency was somewhat reduced in casein-infused
cows. Recently, attention has focused on the relation-
ship between nitrogen utilization in lactating cows and
environmental pollution (Castillo et al., 2000). To avoid
environmental contamination, diets high in NSC and
low in CP have been suggested (Tamminga, 1992).
The goal of this study was to determine the response
to starch infusion into the rumen or the duodenum in
dairy cows maintained on a high-concentrate diet. Cows
infused with water or with the equivalent energy input
as oil to the duodenum served as controls. The effect
of these treatments on nutrient digestibility, nutrient
and metabolic hormone concentrations, milk yield, and
milk energy and protein yield efficiency was inves-
tigated.
MATERIALS AND METHODS
Animals and Management
Four Israeli-Holstein cows in midlactation (DIM =
108 ± 12, BW, 580 ± 38 kg; mean initial milk yield 28
± 3 kg/d) were fitted with flexible ruminal cannula with
an internal diameter of 10 cm, and with a flexible T-
type abomasal cannula with an internal diameter of 2
cm. Three of the cows were also fitted with flexible
T-type ileal cannulas. Cannulas were prepared from
Plastisol (Industrial Arts Supply Co., St. Louis Park,
MN). Blood-sampling catheters (T-10 X HN6.0-35-90-
M-10S-PIG, Teflon, heparin-coated, ID 0.35, COOK,
Bloomington, IN), were placed in the costo-abdominal
artery by the method described by Haibel et al. (1989).
Venous samples were taken from a temporary polyvinyl
chloride catheter inserted in the mammary vein 1 d
before blood sampling started. The patency of catheters
was maintained by daily flushing with sterile heparin-
ized (300 IU/ml) saline (154 mM NaCl). This setup en-
abled measuring of arteriovenous differences in metab-
olites across the mammary gland.
Upon full recovery, cows were used in a 4 × 4 Latin
square experimental design. All cows were housed in
Journal of Dairy Science Vol. 84, No. 2, 2001
Table 1. Composition of the basal diet.
Ingredient (% of DM)
Wheat silage 7.5
Corn silage 14.2
Pea hay 6.5
Wheat hay 3.5
Wheat bran 6.4
Whole cottonseeds 6.5
Corn grain, ground 16.5
Barley grain, rolled 14.0
Corn gluten feed 4.4
Sunflower meal, 37% CP 3.6
Soybean meal,
1
50% CP 4.8
Rapeseed meal, 38% CP 3.2
Citrus pulp 5.7
Calcium carbonate 0.6
Ammonium sulfate 0.4
Vitamins and minerals
2
2.2
NE
L
,
3
Mcal/kg 1.73
OM 92
NSC 29
CP 17
RUP, % of CP 32
NDF 34
1
Solvent extracted and heated soybean meal.
2
Contained 20,000,000 IU/kg of vitamin A, 2,000,000 IU/kg of vita-
min D, 15,000 IU/kg of vitamin E, 6000 mg/kg of Mn, 6000 mg/kg of
Zn, 2000 mg/kg of Fe, 1500 mg/kg of Cu, 120 mg/kg of I, 50 mg/kg
of Se, and 20 mg/kg of Co.
3
Based on NRC (1989).
metabolic stalls, fed a basal diet (Table 1) ad libitum.
The basal diet was mixed in a mixing wagon and pro-
vided as a TMR. Animals were given free access to
water. Feed intake was recorded daily. Treatments con-
sisted of infusion of: 1.5 kg of water into the rumen
(CONT), 1.5 kg of cornstarch (Galam, Israel) emulsion
into the rumen (RS) or abomasum (AS), or 0.5 kg of
corn oil (Milomor, Israel) into the abomasum (OIL).
Solutions were infused for 21 h per 24-h period. Cows
were exercised for 3 h/d in an open yard. Infusion was
stopped during exercise and during short intervals of
sample collections. Infusions were through a plastic
tube, attached to the abomasal cannula, with a peristal-
tic pump (Minipuls 2, Gilson, France). Each experimen-
tal period consisted of 14 d; a 10-d adaptation followed
by4dofsample collection.
Sample Collection and Analyses
Chromium-mordant NDF (2 g of Cr daily) was used
as a marker to determine digesta outflow. The daily
marker dose was administrated in two equal portions
into the rumen cannula. Ruminal, abomasal, ileal, and
fecal grab samples were taken on d 11 to 13 at 2-h
intervals. Samples were stored at –20°C until analysis.
For ruminal ammonia N determination, samples
were mixed with 5 ml of TCA (20%). Blood samples
ARIELI ET AL.464
were withdrawn simultaneously from the mammary
vein and costo-abdominal artery on d 14 on the hour,
from 0800 to 1400 h, and were transferred into heparin-
ized Vacutainers. Heparin (0.5 ml diluted with saline)
was injected into the arterial catheter immediately be-
fore the blood sample was withdrawn. The blood sam-
ples were immediately centrifuged (3000 × g for 10 min)
and the plasma was separated for urea, AA, glucose,
insulin, and IGF-1 analyses. All samples were stored
at –20°C until analysis. For AA analysis, plasma sam-
ples were composited across the 7 sampling times and
stored at –20°C.
Digesta samples were dried at 55°C for 48 h, ground
to pass through a 2-mm screen, and pooled on a DM
basis. Concentrations of nutrients and marker were
determined in a homogenized sample. The DM and OM
contents were determined after drying at 105°C over-
night or ashing at 600°C for 3.5 h. The content of CP
was determined by the Kjeldahl method in a Tecator
Kjeltec auto 1030 analyzer; NDF was determined ac-
cording to Van Soest et al. (1991), and NSC was deter-
mined according to Smith (1981).
Ammonia N content in centrifuged rumen samples
was determined by an autoanalyzer (Technicon Corp.,
Tarrytown, NY) using salicylic acid instead of phenol
(Krom, 1980). Plasma urea was determined according
to Coulomb and Faverau (1963). Glucose was deter-
mined with a Glucose Analyzer (model 2, Beckman).
For plasma-free AA analysis, 0.1 ml of sulfosalicylic
acid (50 g/100 g) was added to 0.9 ml of plasma and
total protein was precipitated by centrifuging at 15,000
× g for 5 min at 4°C (Mikro 12–24 centrifuge, Hettich,
Germany). Amino acids were separated on a reverse-
phase column (Superpher 60 RP 8 (4 mm) Lichro Cart
250-4, Merk, Darmstadt, Germany) by HPLC with 9-
fluorenyl-methyloxycarbonylchloride as the derivatiz-
ing agent. Plasma AA concentration was measured in
pooled 6-h aliquots.
Plasma insulin and plasma IGF-1 were determined
with radioimmunoassay kits (Diagnostic Products
Corp., Los Angeles, CA, and Diagnostic Systems Labo-
ratories Inc., Webster, TX). Chromium content in the
feed, digesta, and feces was determined following wet
digestion, with concentrated nitric acid at high temper-
atures by inductively coupled plasma-atomic emission
spectroscopy in a Spectroflame Spectro Gmbh (Kleve,
Germany) system.
Milk Production and Milk Composition
Cows were milked twice daily at 0600 and 1800 h.
Milk yield was recorded daily by automatic meter
(Afimilk, Afikim, Israel). Milk samples were taken at
each milking during the last 4 d of each measurement
Journal of Dairy Science Vol. 84, No. 2, 2001
period and analyzed for fat, protein, and lactose content
by infrared procedures at the Israel Cattle Breeders
Association, Milk Recording Laboratory (Cesarea,
Israel).
Calculations and Statistical Analyses
Extraction rates of AA and glucose by the mammary
gland were calculated as the difference between arterial
and mammary venous concentrations divided by the
arterial concentration.
Energy balance was calculated as NE
L
intake—main-
tenance requirements—milk energy output. Energy in-
take was based on NRC (1989) tables. The assigned
caloric values for fat, protein, and lactose were 9.3, 5.9
and 4.0 kcal/g, respectively. Maintenance requirements
were estimated according to NRC (1989). Energetic ef-
ficiency was calculated as milk NE
L
yield/(NE
L
intake—
maintenance requirements).
Data were analyzed by ANOVA for the 4 × 4 Latin
square design using the GLM procedure of SAS (1985)
to examine the effects of treatments on metabolites and
hormones concentrations, DMI, nutrient flows and di-
gestibilities, and milk yield and composition. Ileal pa-
rameters were analyzed as 4 × 4 incomplete Latin
square design. Data are presented as least square
means. Significance was declared at P < 0.1. When sig-
nificant effect was found, means were compared using
Student’s t-test.
RESULTS AND DISCUSSION
Nutrient Intake and Digestibility
Ruminal or abomasal infusions of starch were associ-
ated with a respective decrease of 13 and 8% in volun-
tary feed OM intake (Table 2). Reduced voluntary in-
take in dairy cows in response to ruminal or abomasal
starch infusion has been described by Knowlton et al.
(1998a). However, irrespective of infusion site, overall
energy intake, including infusion, was similar in CONT
and starch-infused cows. This indicates that cows were
able to detect, and counterbalance energy that was sup-
plied by the respective starch infusions.
In our study, the daily amount of energy infused as
starch or oil was similar. In OIL cows, the voluntary
intake of feed OM and NE
L
was reduced by 22 and 14%,
respectively. When extra energy was supplied to dairy
cows in the form of inert fat (4% of DM), DMI was
reduced but NE
L
intake was similar to controls (Klus-
meyer et al., 1991). Inclusion of a lower concentration
of inert fat (2% of DM) in dairy cow diets was associated
with an increase in NE
L
intake (Moallem et al., 2000).
Our data agree with those of Gagliostro and Chilliard
(1991), where postruminal infusion of oil was associated
SITE AND SOURCE OF ENERGY SUPPLEMENTATION 465
Table 2. Daily intake of NE
L
and OM, and flow and digestion of OM in the digestive tract of cows.
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
NE
L
Intake, Mcal/d 38.0
a
36.0
a
37.9
a
32.8
b
1.06 0.040
OM Eaten, kg/d 20.3
a
17.6
b
18.6
b
15.9
c
0.57 0.008
OM Intake,
1
kg/d 20.3
a
19.1
a
20.1
a
16.4
b
0.57 0.009
Flow to duodenum, kg/d 13.9 12.2 12.1 10.8 0.94 0.241
Flow to ileum, kg/d 5.6 4.8 4.8 4.2 0.27 0.185
Fecal output, kg/d 7.0 5.9 7.6 5.4 0.54 0.103
Apparent digestibility
2
Rumen, % 32.0 30.4 42.9 35.2 3.37 0.138
Postrumen, % 48.8 51.6 37.0 49.6 5.23 0.285
Small intestine, % 57.5 62.0 58.3 63.0 5.10 0.903
Total tract, % 65.8 69.2 62.4 66.9 2.20 0.275
a,b,c
Means in a row with different superscripts differ (P < 0.1).
1
Including infusion.
2
Percentage of entering.
with reduced intake of DM and NE
L
. The type of added
lipid appeared to affect overall feed intake. A decrease
in NE
L
intake greater than the NE
L
value of the infused
oil might be partially explained by the involvement of
the gut hormone cholecystokinin in feed-intake regula-
tion (Bremmer et al., 1998).
Ruminal starch infusion did not change ruminal NSC
digestibility, which averaged 62% among treatments
(Table 3). Similar ruminal NSC digestibilities were re-
ported by Shabi et al. (1999). Ruminal degradability of
starch from the grains could be lower than that of the
infused starch due to the presence of interfering pro-
teins in the former (Philippeau et al., 2000). The propor-
tion of infused starch in our study was about 20% of
total duodenal NSC flow. It appears that when the basal
diet contains a large amount of NSC, a large proportion
of infused starch may be needed to obtain a significant
increase in ruminal starch digestibility.
Postruminal digestibility of NSC was lower in OIL
than in the other treatments (Table 3). In nonrumi-
Table 3. Daily intake, flow, and digestion of NSC in the digestive tract of cows.
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
NSC eaten, kg/d 6.5
a
5.6
b
5.9
a
5.1
c
0.18 0.083
NSC intake,
1
kg/d 6.5
b
7.1
a
7.4
a
5.1
c
0.18 0.000
Flow to duodenum, kg/d 2.7
b
2.3
b
4.0
a
1.6
c
0.23 0.002
Flow to ileum, kg/d 0.6 0.5 0.6 0.5 0.07 0.632
Fecal output, kg/d 0.5 0.4 0.8 0.5 0.11 0.177
Apparent digestibility
2
Rumen, % 59.3 66.9 57.6 67.7 3.01 0.122
Postrumen, % 78.8
a
84.7
a
80.5
a
63.3
b
4.05 0.048
Small intestine, % 70.7 82.4 81.0 64.2 6.87 0.481
Total tract, % 91.7 94.8 89.8 88.5 1.92 0.211
a,b,c
Means in a row with different superscripts differ (P < 0.1).
1
Including infusion.
2
Percentage of entering.
Journal of Dairy Science Vol. 84, No. 2, 2001
nants, increasing dietary fat concentration may cause
a reduction in amylase activity (Jacobs, 1983). Similar
mechanism may explain the reduced intestinal NSC
digestibility in oil infused cows.
Small intestine NSC digestibility was similar in AS
and in CONT. As only three cows were provided with
an ileal cannula, small intestine digestibility data
should be treated with caution. Nevertheless, the simi-
larity of NSC digestion values in the small intestine
and postruminal sections indicates that, in this study,
starch digestion in the large intestine was rather
limited.
The digestibility of NSC in the small intestine aver-
aged 75% among diets (Table 3). The values of NSC
digestibility in the small intestine found in this study
are within the normal ranges reported in ruminants
(Huntington, 1997). When steers maintained on a com-
plete forage diet were abomasally infused with 1 kg/d of
starch, apparent small intestinal starch disappearance
was 79% (Branco et al., 1999). According to Reynolds
ARIELI ET AL.466
Table 4. Daily intake, flow, and digestion of CP in the digestive tract of cows.
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
CP intake, kg/d 3.2
a
3.1
bc
3.3
ab
2.8
b
0.11 0.018
Flow to duodenum, kg/d 3.4
a
3.2
ab
2.4
c
2.5
bc
0.23 0.063
Flow to ileum, kg/d 0.6 0.9 0.7 0.7 0.12 0.805
Fecal output, kg/d 1.3
a
1.1
ab
1.3
a
0.9
b
0.08 0.078
Apparent digestibility
1
Rumen, % 5.1
b
−1.6
b
28.5
a
11.4
b
5.40 0.048
Postrumen, % 62.4 66.3 43.1 62.0 5.31 0.104
Small intestine, % 84.2 73.1 66.3 71.2 4.07 0.256
Total tract, % 65.2 64.8 61.4 66.6 1.76 0.319
a,b,c
Means in a row with different superscripts differ (P < 0.1).
1
Percentage of entering.
et al. (1997), the maximal anticipated amount of starch
digested in the small intestine of the lactating dairy
cow is 2.4 kg. This value is similar to small intestinal
digestion of NSC in our CONT. Nonetheless, the 3.4
kg/d of NSC digested in AS is comparable to postrumi-
nal NSC digestibility of 4.8 kg/d in dairy cows at a
similar production level (Shabi et al., 1999). Okine et
al. (1994) suggested that glucose transport potential
in the small intestine of lactating cows is related to
metabolic demands set by the mammary gland. Differ-
ences in the adaptation of cattle to dietary energy con-
centrations, energy intake, and energy requirements
might explain the variability in reports concerning the
capacity of small intestinal starch digestion. Results
from the present study emphasize the capacity of high-
producing dairy cows to absorb large amounts of gluco-
genic nutrients through the small intestine.
There were no treatment effects on NDF digestibility;
mean ruminal and total tract NDF digestibilities were
49 and 52% (data not shown). Comparable values were
obtained in dairy cows fed high-concentrate diets (Shabi
et al., 1999). Similar ruminal NDF digestibility among
treatments suggests that fiber fermentation conditions
were not greatly deteriorated by the addition of 1.5 kg
of starch into the rumen. Normal microbial efficiency
values were found when apparent rumen-degradable
OM was 7 to 8 kg/d (Mabjeesh et al., 1996), similar
to the ruminal digestion of OM in the current study
(Table 2).
Intake of CP was decreased in RS by 0.5 kg/d, whereas
CP flow to the duodenum was similar to CONT (Table
4), indicating improved ruminal microbial synthesis in
RS-treated cows. While total tract CP digestibility was
similar among treatments, postruminal CP digestibil-
ity tended to decrease in AS cows. This reduction could
be partially explained by large intestine fermentation
of residual starch (Knowlton et al., 1998b; Orskov,
1986). In addition, an increase in intestinal endogenous
N loss (Tamminga et al., 1995) due to abomasal starch
Journal of Dairy Science Vol. 84, No. 2, 2001
infusion could contribute to the reduced CP digestibility
in these cows.
Milk Yield and Composition
Compared with CONT, yield of milk and its constit-
uents was decreased by OIL treatment (Table 5),
whereas infusion of starch, as RS or AS had no effect.
Efficiency of milk energy production was similar among
treatments. The average efficiency of milk NE
L
produc-
tion was 75%, indicating that cows in this study were
in a state of positive energy balance (averaging 7 Mcal
of NE
L
per day).
The proportions of starch digestion in the rumen or
postruminally may be modified in practice by feed pro-
cessing. A review by Nocek and Tamminga (1991) con-
cluded that starch digested postruminally may be used
more efficiently for milk synthesis than that digested
in the rumen. However, modifications of ruminal degra-
dability of corn obtained by replacing steam-flaked corn
with dry-rolled corn (Crocker et al., 1998), or when corn
grain was supplied in ground or rolled form or as high
moisture grain (Knowlton et al., 1998b), did not result
in a change in milk yield. Of the 6.5 kg/d of NSC digested
in the total tract, 29 and 50% was digested postrumi-
nally in RS and AS cows, respectively. A larger alter-
ation in the site of the digested starch may be needed
to modify the efficiency of milk energy production.
One of our goals was to assess the effect of modifica-
tions in energy supply on efficiency of milk protein pro-
duction. DePeters and Cant (1992) concluded that in-
creasing energy intake will increase both content and
yield of milk protein. Protein production efficiency was
similar among treatments and averaged 27%. Actual
dietary CP concentration (including the infusate) in AS
and RS diets was 15.3%, compared with 16.5% in
CONT. The similarity in milk protein efficiency among
diets indicates that in these cows, protein supply was
adequate. As cows were in positive energy balance, the
SITE AND SOURCE OF ENERGY SUPPLEMENTATION 467
Table 5. Milk yield and composition.
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
Milk, kg/d 27.4
a
26.3
a
26.1
a
23.3
b
0.81 0.051
Fat, % 4.13 4.08 3.86 4.29 0.133 0.245
Protein, % 3.47
a
3.41
a
3.56
a
3.21
b
0.069 0.052
Lactose, % 4.76 4.85 4.85 4.63 0.069 0.181
Fat, kg/d 1.119 1.065 1.006 1.000 0.032 0.120
Prot, kg/d 0.952
a
0.896
a
0.932
a
0.747
b
0.031 0.012
Lactose, kg/d 1.303
a
1.270
a
1.260
a
1.076 0.054 0.083
Milk energy, Mcal/d 21.0
a
20.1
a
19.7
a
17.8
b
0.551 0.031
Energy balance,
1
Mcal/d 7.50 6.40 8.70 5.47 1.130 0.299
Energy efficiency,
2
% 74.0 76.2 69.3 76.9 3.307 0.430
Protein efficiency,
3
% 26.2 28.5 27.9 26.3 0.931 0.284
a,b
Means in a row with different superscripts differ (P < 0.1).
1
Energy balance = NE
L
intake − maintenance requirements − milk energy output.
2
Energetic efficiency = milk NE
L
yield/(NE
L
intake − maintenance requirements).
3
Protein efficiency = milk protein/CP intake.
extra energy that could be obtained from the infused
nutrients was apparently not directed toward reducing
the usage of AA as an energy source. The response of
milk protein to energy supply is higher in early lacta-
tion than in midlactation (Coulon and Remond, 1991).
Because lactating cows adjust to increased exogenous
glucose by increasing glucose utilization without de-
creasing endogenous glucose production (Amaral et al.,
1990), the effect of energy supplementation on milk
protein efficiency should be tested under conditions in
which the supply and requirements of dietary protein
are closely matched.
Metabolite and Hormone Concentrations
About 17% of the overall energy intake was provided
by infusion in the form of starch (RS), glucose (AS), or
FFA (OIL). We hypothesized that the various metabolic
fuels would have diverse effects on metabolic and hor-
monal profiles in the plasma, and thereby would affect
milk production and efficiency. Plasma concentrations
of glucose, insulin, and IGF-1, and mammary gland
glucose extraction rate, were similar among treatments
(Table 6). In high-yielding dairy cows, infusion of starch
Table 6. Plasma glucose, insulin, IGF-1, and urea N concentrations, and rumen ammonia N.
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
Arterial glucose, mg/dl 50.9 51.6 53.9 55.0 2.10 0.52
Glucose extraction rate,
1
% 27.9 28.2 24.1 23.9 4.30 0.40
Insulin, µIU/ml 19.4 18.4 20.6 15.5 1.42 0.18
IGF-1, ng/ml 97 67 81 66 13 0.42
Plasma urea N, mg/dl 11.9 11.3 10.2 11.3 0.71 0.47
Ammonia N, mg/dl 14.9 11.7 13.2 14.6 1.15 0.28
1
Glucose extraction rates = the difference between arterial and mammary venous concentration divided
by the arterial concentration.
Journal of Dairy Science Vol. 84, No. 2, 2001
into the rumen or abomasum did not modify the produc-
tion of milk constituents or plasma glucose, but did
increase insulin concentrations (Knowlton et al.,
1998a). Infusion of fatty acids into the abomasum of
dairy cows did not modify plasma glucose concentra-
tions (Bremmer et al., 1998). Insulin secretion was simi-
lar in dairy cows fed a starch-rich diet or a fat-supple-
mented diet (Blum et al., 1999). Glucose concentration
in the mammary vein was negatively correlated with
milk energy:
Y = 57.6 – 0.95X (r
2
= 0.37; n = 16; P < 0.05)
where Y = glucose concentration in the mammary vein
(mg/100 ml), X = milk NE
L
(Mcal/d).
This relationship, and the relatively uniform glucose
concentrations in the peripheral plasma in the afore-
mentioned studies is in line with the low insulin-medi-
ated glucose uptake, versus large noninsulin-mediated
glucose uptake by the mammary gland (Rose et al.,
1997). In the present study, no significant correlation
was found between milk yield and insulin concentra-
tion. However, insulin concentrations were positively
correlated with energy balance:
ARIELI ET AL.468
Table 7. Concentration of essential AA in the arterial plasma of cows.
1
Starch via Starch via Oil via
Control rumen abomasum abomasum SEM P <
µM
Thr 87.1 86.3 94.2 69.7 7.0 0.188
Met 25.5 27.1 26.2 23.4 2.2 0.688
Val 192.4 210.7 199.9 206.7 7.6 0.413
Phe 61.1 67.0 60.9 71.7 5.5 0.510
Ile 100.1 104.2 102.8 112.1 3.6 0.209
Leu 118.7 130.1 130.0 142.1 6.2 0.172
His 40.7 48.8 60.5 45.4 7.9 0.402
Lys 93.2 88.1 78.0 99.9 5.7 0.148
1
Extraction rates = the difference between arterial and mammary venous concentrations divided by the
arterial concentration.
Y = 13.3 + 0.76X (r
2
= 0.34; n = 16; P < 0.05)
where Y = insulin concentration (units/ml), X = NE
L
balance (Mcal/d).
A concomitant increase in milk production and mam-
mary gland nutrient supply can be promoted via mam-
mary tissue adaptation, controlled by the somatotropin/
IGF system (McGuire et al., 1995). Blum et al. (2000)
reported that the concentration of IGF-1 is lower in
cows fed lipids than in cows fed a starch-rich ration. In
the present study, IGF-1 concentrations were similar
among treatments, and no correlation was found be-
tween it and milk yield or energy-balance parameters.
The lack of response in milk yield to the additional
starch supply in RS and AS treatments in the present
study might be explained by the positive energy balance
and low activity of the somatotropin/IGF system in
cows.
The observed extra 1.0 kg/d of starch digested in the
rumen in RS versus CONT cows could cause a decrease
in ammonia concentration. No effects on rumen ammo-
nia or plasma urea concentrations were observed when
cows were infused with 1.1 kg/d of glucose (Wu et al.,
1994). The concentrations of ruminal ammonia and
plasma urea in the present study were lower than re-
ported by Wu et al. (1994), in line with the respective
Table 8. Plasma net extraction
1
of essential AA by the mammary gland.
Starch Starch Oil
Infusion Control rumen abomasum abomasum SEM P <
%
Thr 61.5 58.9 58.6 62.9 4.6 0.886
Met 68.0 65.8 67.3 66.1 9.4 0.998
Val 58.6 54.1 53.1 56.3 2.7 0.521
Phe 57.9 60.3 63.2 53.0 5.0 0.484
Ile 67.7 63.8 63.0 88.5 3.4 0.750
Leu 70.3 73.5 75.7 71.9 2.0 0.348
His 52.4 58.0 59.3 71.5 11.2 0.689
Lys 75.8 76.8 74.8 75.3 3.4 0.977
Journal of Dairy Science Vol. 84, No. 2, 2001
differences in the ratio of rumen available carbohydrate
to rumen available nitrogen.
Arterial concentration and mammary extraction
rates of essential AA (EAA, Tables 7 and 8) were similar
among treatments. Insulin clamp treatments, which
resulted in increased milk protein yield, markedly de-
creased the plasma concentration of most EAA and in-
creased the extraction efficiency of some EAA (Mackle
et al., 2000). In that study, milk protein yield was not
related to either arterial concentration or the arteriove-
nous difference for all EAA. Mackle et al. (2000) con-
cluded that other regulatory elements should be consid-
ered to adequately characterize AA use in milk protein
synthesis. Besides directly affecting nutrient supply to
the mammary gland, exogenous glucose supply (from
intestinally infused starch directly, or from propionate-
induced gluconeogenesis in cows infused with starch
ruminally) could spare nonmammary AA utilization,
thereby improving mammary AA supply and utiliza-
tion. Meijer et al. (1997) studied the effect of starch
infusion site on AA availability in dairy cows, while
trying to reduce the loss of AA in splanchnic tissues by
increasing the overall energy supply. The conclusion
was that when supply is at or above energy and protein
requirements, extra starch supply to the duodenum
does not affect AA utilization by the splanchnic tissue.
SITE AND SOURCE OF ENERGY SUPPLEMENTATION 469
In contrast, other means such as the use of bovine soma-
totropin, were predicted to reduce dairy cows N excre-
tion per unit of milk by 8% (Dunlap et al., 2000). Other
modeling work (Castillo et al., 2000) showed that almost
all the N in excess of lactating dairy cows requirements
will be excreted in urine. Castillo et al. (2000) concluded
that a decrease in N excretion by dairy cows can be
attained by reduction in N intake according to animal
requirements. Further research is needed to determine
the efficiency of milk energy and protein yield in re-
sponse to starch infusion into the rumen or into the
duodenum in high yielding lactating dairy cows main-
tained on a high-concentrate diet.
CONCLUSIONS
Large amounts of starch can be efficiently digested
in the rumen or small intestine of dairy cows. In dairy
cows maintained on high concentrate diets, infusion of
1.5 kg/d of starch into the rumen might increase CP
duodenal flow. Infusing the same amount of starch into
the abomasum decreases apparent postruminal CP di-
gestibility. There appears to be no metabolic advantage
to increasing the supply of starch to the rumen or abo-
masum of midlactation dairy cows. In these cows, pro-
duction and efficiency of milk constituent yield appear
not to be limited by the supply of energetic or nitroge-
nous nutrients.
ACKNOWLEDGMENTS
This research was support by a grant from the United
States-Israel, Binational Agriculture Research and De-
velopment Fund (BARD), No. US-2642-95.
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