1. No category

Effects of Protein and Energy Supplementation of Cows Grazing
Native Winter Range Forage on Intake and Digestibility
R. J. Kartchner
J ANIM SCI 1980, 51:432-438.
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EFFECTS OF PROTEIN AND ENERGY SUPPLEMENTATION OF COWS
GR A Z I NG NA T I VE WINTER RANGE FORAGE ON
INTAKE AND DIGESTIBILITY
R. J. Kartchner
Livestock and Range Researcb Station I , Miles City, MT 59301
Summary
Trials were conducted in November and
December of 1976 (trial 1) and in 1977 (trial
2). A daily equivalent of .75 kg of cottonseed
meal (trial 1) or .70 kg of soybean meal (trial
2) was fed individually at 2- or 3-day intervals
to dry, pregnant, mature cows grazing native
fall-winter range (treatment P). Cracked
barley (treatment G) was fed to a second
group of cows at levels isocaloric with treatment P. A third group (treatment C) served as
a control and received no supplement. Forage
dry matter intake (DMI) and digestibility
(DMD) were determined with chromic oxide
and lignin used as indicators. In trial 1, with
s e v e n cows per treatment, forage DMI for treatments C, P and G were 8,639, 8,157 and
7,851 g/day, respectively. Respective values for
forage DMD were: 54.9, 52.9 and 51.7%; for
total DMI: 8,639, 8,898 and 8,537 g/day; and
for total DMD: 54.9, 53.2 and 54.2%. All differences were nonsignificant. Average total
weight gains for treatment groups ranged from
15.0 to 16.8 kg per animal. In trial 2, with 11
cows per treatment, daily forage DMI was
higher for cows receiving treatment P (8,009
g; P<.O1) than for those receiving treatment C
(6,813 g) or G (6,305 g). Forage DMD was
lower for G (34.3%; P<.O1) than for C (40.6%)
or P (43.6%). Daily DMI was 6,813 g for cows
receiving treatment C, 8,684 g for those rece]w
ing treatment P and 6,961 g for those receiving
treatment G (P<.O1 for P vs C and P vs G);
DMD for respective treatments was 40.6,
46.4 and 38.8% (P<.O1 for P vs C and P vs G).
Treatment differences in weight change ( - 1 5 . 3
to - 2 1 . 2 kg per animal) and changes in body
condition score were not significant. Differ-
ences in forage DMI and DMD and response to
supplementation between years were attributed
to quantity and quality of forages available to
the animals.
(Key-Words: Beef Cattle, Winter Supplementation, Protein Supplement, Energy Supplement,
Forage Intake, Forage Digestion.)
Introduction
Providing protein and energy supplements to
range cattle during periods of drought or winter
is a widespread practice among livestock producers. However, results of controlled experiments designed to determine the effects of
supplemental feeding have been variable. Early
work on the effects of protein supplements
provided to wintering range cattle in Montana
showed considerable y e a r - t o - y e a r variation.
Response was greatest during severe winters
when forage availability was limited (Black et
al., 1938). McCall (1940) was able to enhance
digestibility and intake of a mixture of mature
range grasses by feeding a protein meal supplement, but digestible energy intake was greatest
when a barley supplement was fed. Rittenhouse
et al. (1970) found little effect of protein supplementation on forage intake and digestibility.
Energy supplementation depressed forage intake but did not affect forage digestibility.
Cook and Harris (1968) found that protein
supplements tended to enhance intake and
digestibility of winter forage by cattle and
sheep, whereas energy or energy plus protein
generally had no effect or tended to decrease
intake and digestion. Speth et al. (1962) supplemented cows during the winter on a browseshrub range where energy was limiting with
either .45 k g . o f barley or .45 kg of protein
cake. Both groups maintained body weight or
gained slightly, whereas nonsupplemented cows
l Jointly operated by SEA, AR, USDA and Mon- lost weight. Cows fed barley weaned more
calves than did either control cows or cows
tana Agr. Exp. Sta., Montana State Univ. Montana
Agr. Exp. Sta. Tech. Paper No. J969.
fed protein. In contrast, Bellows and Thomas
432
JOURNAL OF ANIMAL SCIENCE, Vol. 51, No. 2, 1981
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FORAGE INTAKE AND DIGESTIBILITY
(1976) noted a decrease in the fall pregnancy
rate of cows fed 3.86 kg of barley either
before or during lactation or before and during
the breeding season compared with the pregnancy rate of cows grazing range forage only.
Feeding barley resulted in reduced grazing time
and apparently served to replace forage rather
than supplement it.
Results of these studies show a need for additional work to clarify relationships among
protein or energy supplementation and forage
dry matter intake (DMI), forage dry matter
digestibility (DMD) and livestock performance.
The present study was conducted to examine
the effects of feeding supplemental protein or
energy during the fall and winter on DMI and
DMD of mature range forage.
Materials and Methods
Two trials were conducted. Both trials were
ended in the mid- to latter part of December
because heavy snow cover precluded continued
grazing.
Trial 1. The first trial ran from November 10
to December 17, 1976. Twenty-one dry,
pregnant Hereford cows (3 to 6 years old,
average weight 458 kg) were randomly allotted to one of three treatments: (a) control,
no supplement provided; (b) protein, 1.5 kg
cottonseed meal (IRN 5-01-621) fed individually on alternate days, and (c)grain, 1.4
kg cracked barley (IRN 4-00-549) fed individually on alternate days. The protein fed
was calculated to supply 75% of the crude
protein requirements for a 450- to 500-kg
cow in the middle third of pregnancy (NRC,
1976). The grain fed was calculated to be isocaloric with the protein meal and, in addition,
to supply approximately 20% of the animal's
protein requirement. Nine esophageally-fistulated cattle were randomly allotted to the same
treatments and supplemented on the same
schedule as the other cows.
On days when supplements were fed, all
cows, including controls, were gathered and
tied up; supplemented cows were fed individually with buckets. After supplemented
cows had finished eating, all cows were released and allowed to return to pasture. Cows
were weighed at the beginning and end of the
experimental period. Before and during the
study, the cows were grazed on native range.
No supplemental vitamin A was provided,
but a salt-dicalcium phosphate-trace mineral
mix was available at all times.
433
The study was conducted on 128 ha of a
broken upland range site. The major grass
species in the test area included blue grama
(Bouteloua gracilis), western wheatgrass (Agropyron srnitbii), needle and thread grass (Stipa
comata) and buffalograss (Bucbloe dactyloides).
Major browse species included greasewood
(Sarcobatus vermiculatus), shadscale (Atriplex
confert~/blia), Gardner's saltbush (Atriplex
gardneri) and winterfat (Ceratoides lanata).
Big sagebrush (Arternesia tridentata wyomingensis) and silver sagebrush (Artemesia cana)
were also prominent among the shrub species
but, except under adverse conditions, the
cattle appeared to graze these species little
or not at all. Forbs were generally not available
at this time of year.
Forage DMI and DMD were determined with
chromic oxide as an external indicator and
lignin as an internal indicator. Starting on
November 29, 20 g of chromic oxide in a
gelatin capsule were administered orally with
a bailing gun once daily to each cow for a 9day preliminary dosing period and a 10-day
fecal sampling period. A fecal grab sample was
taken at the time the chromic oxide was
administered. Two cows from each treatment
group were fitted with total collection fecal
bags for the last 4 days of the intake trial for
estimation of chromic oxide recovery.
Twice-weekly esophageal fistula samples
were collected on days alternate to feeding
days starting on November 30 and continuing
through December 16. Fistula samples were
collected in the morning after cattle had been
kept off feed over night. All forage and fecal
samples were dried at 45 C and ground through
a 1-mm screen in a Wiley mill in preparation
for chemical analysis.
Individual fistula-forage samples were analyzed for Kjeldahl nitrogen and two-stage in
vitro DMD (Tilley and Terry, 1963). Forage
samples were composited across animals and
treatments within day of collection and were
analyzed for acid detergent fiber and acid
detergent lignin according to procedures of
Goering and Van Soest (1970). Fecal samples
were analyzed for acid detergent lignin and
chromic oxide (Kimura and Miller, 1957);
forage, supplement and fecal samples were
analyzed for cellulose as described by Crampton and Maynard (1938). Supplements were
also analyzed for acid detergent lignin. An
example of the method used for calculating
DMI and DMD of cows fed supplements is
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434
KARTCHNER
shown in table 1. Data were subjected to
analysis o f variance, and t r e a t m e n t means
were c o m p a r e d by Duncan's new multiple
range test (Steel and Torrie, 1960).
Trial 2. The second trial was c o n d u c t e d f r o m
N o v e m b e r 2 to D e c e m b e r 23, 1977, on a 4 2 2 ha pasture with vegetation characteristics similar to those o f the pasture described in trial 1.
T r e a t m e n t s were similar to those used in trial
1, e x c e p t that soybean meal ( I R N 5 - 0 4 - 6 0 4 )
was fed to supply 75% of the animal's protein
requirements and barley fed was calculated to
be isocaloric with the soybean meal. The supplemental feeding schedule was adjusted to
a M o n d a y - W e d n e s d a y - F r i d a y sequence. S o y bean meal was fed at a rate o f 1.5 k g / c o w on
Mondays and Wednesdays and 2.0 k g / c o w on
Fridays; barley was fed at a rate of 1.3, 1.3
and 2.0 k g / c o w on those 3 days. S u p p l e m e n t e d
cows were put into individual stalls, and the
s u p p l e m e n t was fed in buckets.
T h i r t y - t h r e e dry, pregnant Hereford cows
(4 to 9 years old, average weight 497 kg)
were r a n d o m l y allotted to the three treatments.
Twelve esophageally-fistulated cattle were also
r a n d o m l y assigned to t r e a t m e n t s and supple-
m e n t e d in the same m a n n e r as the o t h e r cows.
All animals were weighed at 1 4 - d a y intervals
starting on N o v e m b e r 2. Before the experiment, c o w s ' teeth were checked and only those
cows with good teeth were included in the
project. All cows selected were then given an
injection of 1.5 million units o f vitamin A and
c o n d i t i o n scored by two technicians working
i n d e p e n d e n t l y at both the initial and final
weighings. Body c o n d i t i o n was rated on a scale
of 1 (thinnest) to 10 (fattest). The sum of the
two evaluations provided a numerical c o n d i t i o n
score for each cow.
Twice during trial 2, snow depth required
that hay be fed. The dates and a m o u n t s of hay
fed are listed in table 2. No a t t e m p t was m a d e
to separate cows by t r e a t m e n t when hay was
fed, although supplements were fed on schedule.
An a t t e m p t was made to regulate the a m o u n t
of hay fed so that it would s u p p l e m e n t the
available forage and not substitute for grazing.
Starting on D e c e m b e r 14, cows were given
15 g of chromic oxide daily for a 5-day preliminary dosing and a 5-day fecal sampling
period. Because of adverse weather conditions,
esophageal fistula samples were collected only
TABLE 1. SAMPLE CALCULATION FOR DETERMINING FORAGE DRY MATTER
INTAKE (DMI) AND DIGESTION (DMD) AND TOTAL DIET DMD OF COWS
item
Calculation
Value
Chromic oxide given, g/day
Chromic oxide in feces, g/ga
Fecal output, g/day
Supplement fed, g/day
Supplement digestibilityb
Fecal output from supplement, g/day
Fecal output from forage, g/day
Lignin in feces, %
Lignin in feces, g/day
Lignin in supplement, %
Lignin in supplement, g/day
Fecal lignin from forage, g/day
Fecal lignin from forage, %
Lignin in forage, %
Forage digestibility
Forage intake, g/day
Total intake, g/day
Lignin in diet, %
Total diet digestibility
Forage digestibility, %
Total diet digestibility, %
A
B
C = A/B
D
E
F = D X (1.0 - E)
G = C-F
tt
i =C X H
J
K=D XJ
L = I-K
M = L/G X 100
N
P = 1-(N/M)
Q = G/1-P
R=D+Q
S = i/R • 100
T = 1-(S/H)
U = 100 • P
V = 100 • S
20.0
.0045
4,444
686
.81
130
4,314
11.26
500
3.74
26
474
10.99
5.29
.5186
8,961
9,647
5.15
.5426
51.86
54.26
aAdjusted to 100% recovery of Cr 203 .
bFrom NRC (1976) tables.
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FORAGE INTAKE AND DIGESTIBILITY
TABLE 2. DATES AND AMOUNTS OF HAY
FED TO COWS IN 1977 (TRIAL 2)
Date
Hay fed a,b
kg/head
November 25
November 27
November 28
December 5
December 6
December 7
December 8
December 9
December 10
December 11
December 12
December 13
4.5
4.5
2.0
4.5
4.5
5.6
6.7
8.4
8.4
8.4
4.5
4.5
apoor quality grass-alfalfa hay (IRN 1-08-741)
containing 8.3% crude protein (dry basis).
ball cows fed as a group.
on N o v e m b e r 1 and 8 and D e c e m b e r 21.
Sample p r e p a r a u o n and analysis and t r e a t m e n t
of data were as described for trial 1.
Results
Trial 1. T r e a t m e n t differences were not
significant for any o f the variables measured
(table 3). Total forage DMI and intake per
unit o f m e t a b o l i c size (grams/kilogram-75)
tended to be lower for both groups of supp l e m e n t e d cows than for controls, although
t r e a t m e n t differences in total DMI were smaller
than those for forage alone. Those smaller
differences suggest that both protein and grain
were replacing forage rather than s u p p l e m e n t -
435
mg it. Forage DMD also tended to be lower in
supplemented cows, but total diet DMD varied
little a m o n g treatments.
Forage cellulose
digestion f o l l o w e d the same pattern as forage
DMD. Cows in all t r e a t m e n t s gained weight
during the study.
Chemical c o m p o s i t i o n of fistual-collected
forages is shown in table 4. The N R C (1976)
r e c o m m e n d s that diets for dry, pregnant,
mature cows contain a m i n i m u m of 5.9%
crude protein. Crude protein c o n t e n t o f samples collected in late N o v e m b e r and early
D e c e m b e r exceeded this level (6.1 and 7.0%),
but samples collected in m i d - D e c e m b e r were
slightly deficient (5.2 and 5.6%). A high percentage of browse in the diet was t h o u g h t to
be responsible for the relatively high protein
and lignin c o n t e n t and low digestibility of
the D e c e m b e r 3 forage sample, as suggested
by the data of Van D y n e et al. (1965). Although there were periods o f light snow cover,
snow depth did not appear to limit forage
DMI, but l o w - g r o w i n g grasses such as blue
grama and buffalograss might have been covered for periods of 1 to several days.
Trial 2. Weather conditions were considerably m o r e severe during trial 2 than during
trial 1, with e x t e n d e d periods of cold (range
for D e c e m b e r : - 2 to 38 C) and heavy snow.
During these periods, the cows browsed substantial a m o u n t s of big and silver sagebrush.
Differences in weight loss among t r e a t m e n t
groups were relatively small and nonsignificant,
ranging f r o m a 15.3-kg loss per animal a m o n g
p r o t e i n - f e d cows to a 21.2-kg loss among
grain-fed cows (table 3). Cows in all three
t r e a t m e n t groups showed similar weight change
TABLE 3. DRY MATTER INTAKE (DMI), DIGESTIBILITY (DMD) AND COW
PERFORMANCE ON FALL -WINTER RANGE
Trial I
Trial 2
Item
Control
Forage DMI, g/day.
Forage DMI, g/kg'75/day
Forage DMD, %
Total DMI, g/day
Total DMD, %
Cellulose digestion, %
Body weight change, kg
Condition score change
8,639
8,157
7,851
84.1
80.0
78.5
54.9
52.9
51.7
8,639
8,898
8,537
54.9
53.2
54.2
66.6
64.7
63.9
15.4
16.8
15.0
. . . . . . . . .
Protein
Grain
Control
Protein
Grain
6,813 a
66.2 a,b,c
40.6 a
6,813 a
40.6 a
64.3 a,b
- 18.3
- 1.7
8,009 b
76.8 b,d
43.6 a
8,684 b
46.4 b
67.2 a
- 15.3
- 1.4
6,305 a
63.6 a
34.3 b
6,961 a
38.8 a
61.8 b
21.2
1.8
a'bTreatment means on same line within trial bearing different superscripts differ (P<.OI).
C'dTreatment means on same line within trial bearing different superscripts differ (P<.05).
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KARTCHNER
436
TABLE 4. CHEMICAL COMPOSITION AND IN V I T R O DIGESTIBILITY OF FORAGESa
CONSUMED BY FISTULATED CATTLE
Item
Nov. 30
Crude protein, %
Acid detergent fiber, %
Acid detergent lignin, %
In vitro digestion, %
6.1
46.9
5.5
57.1
1976
Dee. 3
Dec. 10
7.0
47.8
6.3
51.2
5.2
49.8
4.9
61.0
Dec. 16
Nov. 1
1977
Nov. 8
5.6
46.9
4.5
59.3
9.4
48.0
8.0
49.2
8.5
51.3
8.2
48.2
Dec. 20
6.5
54.0
12.1
50.6
aDry matter basis.
patterns, although the magnitude of change
varied among treatments. Generally, cows
maintained their weight or gained slightly
during the first weigh period, suffered substantial weight losses during the second and third
weigh periods and maintained or increased
their weight during the last weigh period. There
was considerable variation in individual performance. Six cows - including one from the
grain, two from the control and three from the
protein treatment groups - registered small,
positive net weight changes over the study
period. Changes in condition score followed
the same treatment pattern as changes in
weight, but differences were not significant.
Daily forage DMI tended to be lower for
grain-fed cows (6,305 g) than for control
cows (6,813; P>.05) but was lower (P<.01)
for both groups than for protein-fed cows
(8,009 g). Forage DMI per unit of metabolic
size was also higher for the protein-fed cows
than for either control (P<.05) or grain-fed
(P<.01) cows. Total daily DMI differed little
between control and grain-fed cows (6,813
vs 6,961 g, respectively) but was highest (8,684
g; P<.01) for the protein-fed cows.
Forage DMD was lower (P<.01) in grainfed cows (34.3%) than in control (40.6%) and
protein-fed cows (43.6%). The feeding of protein tended to increase forage DMD over that of
controls, but differences were not significant.
The combined digestibility for forage and
protein meal (46.4%) was higher (P<.01) than
that for forage alone (40.6%) or for grain and
forage (38.8%); the latter two digestibility
values did not differ (P>.05). Forage cellulose
digestibility for the control treatment was intermediate to forage cellulose digestibilities for
the supplemented treatments and did not differ
(P>,05) from either. The 5.4 percentage unit
difference in cellulose digestibility between the
supplemented treatments (67.2% for protein
vs 61.8% for grain) was significant.
Discussion
Results of trial 1 suggest that no advantage
was gained from supplying protein or low levels
of grain to cows under the conditions studied.
Weather conditions were relatively mild, forage
availability was not limiting and a variety of
grass and browse species was available.
The lack of response to added protein shows
that protein was not a limiting factor for either
forage DMI or DMD. This finding agrees with
those of Rittenhouse e t al. (1970), who found
little effect of protein supplementation on
forage DMI and DMD. Forage DMI tended to
be lower in the Rittenhouse et al. (1970) study
(range of 33 to 68 g/kg "75) than in the present
study. Forage DMD in trial 1 was also higher
than that reported by Rittenhouse e t al. (1970).
In contrast to the results of trial 1, DMI and
DMD of consumed forage were markedly affected by supplemental protein and grain in
trial 2. Forage DMD was substantially lower
than that in trial 1 for all treatments. Forage
DMI was somewhat lower in trial 2 than in
trial 1 for control and grain treatments but
differed little for the protein treatments. As
table 4 shows, protein in fistula samples remained high, at 6.5%, in the latter part of
December. However, lignin was also high as a
result of the high proportion of browse in the
diet. In v i t r o digestibility of grazed forages
remained fairly consistent and was substantially
higher than that measured by lignin ratio in the
cows. A similar, though smaller, discrepancy
between in v i t r o and lignin ratio digestibility
values was observed in trial 1.
Exhancement of DMI and DMD of low
quality forages by the feeding of protein has
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FORAGE INTAKE AND DIGESTIBILITY
been observed by other workers. Lyons e t al.
(1970) fed barley straw to steers and found
that.feeding a protein supplement that resulted
in a dietary protein level of 5.82% increased
straw intake by 23% over that of steers fed a
diet containing 4.83% protein. Higher levels
of protein in the diet did not enhance straw
intake over that observed with 5.82% protein.
Elliott (1967) also found that intake of hay
containing 3.4% crude protein increased when
digestible protein was increased from 1.3
g/kg "75 to 2.6 g/kg "75. Hay intake increased
only slightly when digestible protein was
further increased to 3.9 g/kg "75.
In range work, Cook and Harris (1968)
found that protein supplements tended to
enhance both DMI and DMD of range forage,
whereas grain supplements had a negative
effect on both. Similar supplement effects on
fiber digestibility, also noted by Cook and
Harris (1968), agree with the cellulose digestion
data from our trial 2 (table 3).
Other workers have shown that supplementing low quality forages with grain can depress
forage DMI and DMD. Murdoch (1964) found
that intake was depressed more by supplemental concentrates when better quality hays
were fed than when poorer quality hays were
fed. The same trend was observed in our study,
although differences were not significant. The
difference in forage DMI between control and
grain-supplemented cows was 5.6 g/kg "75 in
trial 1 and 2.6 g/kg "75 in trial 2.
Andrews e t al. (1972) and Elliot (1967)
found that the depressing effect of supplemental energy concentrate on forage DMI was
greatest at the lowest protein levels. In trial 2
of our experiment, protein levels as a percentage of the diet did not appear to be limiting
on the basis of protein analysis of fistulacollected forage samples, although forage DMD
tended to be enhanced by the added protein.
Forage DMD for grain-supplemented cows was
6.3 percentage units lower than for controls,
indicating that protein was not adequate or
that other factors were affecting DMD. In the
work of Lyons e t al. (1970), digestibility was
depressed only at the lowest protein level. In
our work, the fact that forage DMI or DMD
was enhanced by protein supplementation and
depressed by grain supplementation with an
apparently adequate dietary protein level may
have been a result of low protein digestibility,
or the forage sample collected from fistulated
cattle may not have been representative of
437
the forage consumed by the rest of the animals.
In spite of the lower forage DMI and DMD
noted for grain-fed cows than for control cows
in trial 2, total DMI and DMD varied little between the two treatment groups. This was
reflected in the relatively small treatment
differences in body weight change and condition score. A greater difference in animal
performance might have been expected between the control and grain-fed cows and the
protein-fed cows on the basis of total DMI
and DMD. Digestible energy (DE) intake can
be calculated from the equation: Kcal DE/g
DM = .18 + .038 DMD (Rittenhouse e t al.,
1971). Accordingly, DE intakes for control,
protein-fed and grain-fed cows in trial 2
were 11.74, 16.87 and 11.52 Mcal/day, respectively, representing an average DE increase
of 45% for protein-fed cows over controls.
Feeding hay for 9 days before the beginning of
the intake trial might have masked some of
the differences in weight changes that might
have been present had no hay been fed. Also,
as noted by Lonsdale e t al. (1971), differences
in carcass weight gains may not be detectable
from animal weights because of differences in
rumen flU. This effect would be exacerbated
by the inherent variability among animals and
the limited number of animals in each treatment group. In this study, changes in condition
score, although not significant, tended to be
more closely correlated with differences in DMI
and DMD than were weight changes.
These data suggest that providing a protein
supplement to range cattle grazing a mixed
shrub-grass vegetation in the Northern Great
Plains during the fall-winter period may
enhance forage DMI and DMD under certain
conditions of forage quality and availability.
This was especially true during periods of
severe winter conditions, when grass availability was limited and shrubs constituted a
substantial proportion of the diet. Under the
same conditions, the feeding of a low level of
barley (approximately .7 kg/day) provided no
apparent benefits in comparison to the feeding
of no supplement; however, the only apparent
negative effects of including the supplement are
in the cost of purchasing and feeding the grain,
because total DE and performance of grain-fed
and control cattle were similar.
Under relatively mild fall-winter conditions
when forage availability was not limiting (as in
trial 1), providing either protein meal or low
levels of grain had neither beneficial nor de-
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43 8
KARTCHNER
l e t e r i o u s effects o n forage DMI, DMD or
a n i m a l p e r f o r m a n c e in c o m p a r i s o n to t h e
feeding o f n o s u p p l e m e n t . This f i n d i n g agrees
w i t h t h a t o f Black e t al. ( 1 9 3 8 ) , w h o c o n d u c t e d
a 5 - y e a r p r o t e i n s u p p l e m e n t s t u d y at this
station. They reported that the benefit from
s u p p l e m e n t a t i o n was greatest d u r i n g severe
winter
range c o n d i t i o n s . Results r e p o r t e d
h e r e i n p r o v i d e insight i n t o w h y t h e r e are
d i f f e r e n c e s in r e s p o n s e to s u p p l e m e n t a t i o n
u n d e r differing range c o n d i t i o n s . However,
f u r t h e r w o r k is n e e d e d to d e l i n e a t e t h o s e
conditions under which supplements provide
b e n e f i t s a n d w h a t c o m b i n a t i o n s a n d levels o f
p r o t e i n a n d e n e r g y best m e e t t h e n e e d s o f lives t o c k w i n t e r i n g o n range.
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