164
Bernard
and Scientist
Carlisle 15:164–168
The Professional
Animal
of Concentrate Feeding
Effect
Level on Production of
Holstein Cows Grazing
Winter Annuals
J. K. BERNARD*,1, PAS, and R. J. CARLISLE†
*Department of Animal Science, The University of Tennessee, Jackson, TN 38237 and †Ames
Plantation, Grand Junction, TN 38039-0389
Abstract
pasture is available in adequate
quantities, metabolizable energy is
the most limiting for milk production (10). Previous research has
demonstrated a positive response in
milk production to concentrate
supplementation for lactating dairy
cows grazing cool season perennials
(3, 13, 15). Similar data are not
available for winter annual forages,
such as annual ryegrass, that are used
more extensively in the southeastern
U.S., where other cool-season annuals are not well-adapted.
Winter annual forages contain
high concentrations of digestible
nutrients throughout the normal
grazing season in the Southeast.
However, the high NDF content of
ryegrass has been shown to limit
intake compared to other forages (7).
During the spring when these winter
annuals are growing rapidly and
quality is high, dairy producers graze
these forages. Conceivably, those
dairy producers who use pasture as
the only forage in the lactating cow’s
Many dairy producers use pasture
diet could reduce the amount of
to provide a portion or all of the
concentrate fed to increase income
forage fed to lactating cows as a
over concentrate cost. However, the
means of reducing feed cost and
amount of concentrate needed to
improving net returns. Conrad and
support the optimum level of milk
Keuren (5) reported that properly
production has not been examined
managed pasture could support up to under these conditions. The objective
20.2 kg of milk/d without supplemen- of this trial was to determine the
tal concentrate. When high quality
response of lactating dairy cows
creased. A quadratic response was
observed for yield of milk fat and protein
A replicated randomized block trial
as yield of these components increased up
was conducted to determine the response to 1:5 and then reached a plateau.
of Holstein cows rotationally grazing
Concentrate DMI in 1997 averaged 0,
annual ryegrass-Crimson clover pasture
4.4, 6.1, and 10.5 kg/d for 0, 1:7, 1:5,
to supplemental concentrate. Within each and 1:3 treatments, respectively. Yields
of 2 yr, 16 Holstein cows were assigned
of milk and milk protein, lactose, and
to one of four blocks by energy-corrected
solids-not-fat increased linearly as the
milk yield, days in milk, and parity.
amount of concentrate fed increased.
Treatments included one of four levels of Regression analysis predicted that
concentrate based on the following grain
pasture alone would support milk yields
to milk ratios: 0 kg concentrate or 1 kg
of 20.4 kg and that the increase in milk
for each 7, 5, or 3 kg of energy-corrected
yield diminished with each increase in
milk. Average chemical composition (DM amount of concentrate fed. These data
basis) of pasture during each grazing
indicate that the amount of concentrate
season was 22.5% DM, 18.5% CP, and
fed when high quality annual ryegrass21.5% ADF in 1996 and 23.5% DM,
crimson clover pasture is readily avail14.6% CP, and 25.2% ADF in 1997.
able can be limited to 1 kg for each 4.5
Concentrate DMI averaged 0, 4.4, 6.2,
kg of energy-corrected milk to optimize
and 8.3 kg/d for 0, 1:7, 1:5, and 1:3
income over concentrate cost.
treatments in 1996, respectively. Yield of
milk and components increased linearly
(Key Words: Grain to Milk Ratio,
as the amount of concentrate fed inMilk Yield, Pasture.)
Introduction
1To
whom correspondence should be addressed: [email protected].
Present address: University of Georgia, Department of Animal & Dairy Science, Coastal
Plain Experiment Station, P. O. Box 748, Tifton,
GA 31793-0748.
Reviewed by L. Brown and L. L. Wilson.
165
Concentrate Feeding with Pasture
grazing annual ryegrass-clover pastures to increasing amounts of
supplemental concentrate.
TABLE 1. Chemical analysis of pasture and concentrate.
Pasture
Materials and Methods
Approximately 4.9 ha were seeded
with 28.0 kg/ha Marshall ryegrass
(Lolium multiflorum) and 16.8 kg/ha
crimson clover (Trifolium incarnatum)
in the fall using no-till practices on
Lexington soil in 1995 and 1996.
Pastures were fertilized with 67 kg/ha
N at seeding and 78 kg/ha in the
spring. Phosphorus and potassium
were applied each year according to
soil test recommendations. Pastures
were divided into six equal paddocks
and rotationally grazed after adequate amounts of forage were
available each spring. Rotation
schedules were based on forage
availability. In 1996, grazing began
on April 18 and continued through
May 23, and in 1997, grazing began
on April 7 and continued through
May 11. Cows were maintained on
pasture except during milking.
Samples of pasture were collected
from six 0.5 m2 locations before and
after grazing for analysis of DM, CP,
(1), ADF (6), NDF (14), Ca, P, Mg, K
(1), and IVDMD (18). Concentrations
of NEl in concentrate [Penn State
Forage Testing Service as reported by
Bath et al. (2)] and pasture (4) were
calculated using average chemical
values.
Within each year, 16 Holstein
cows were assigned to one of four
blocks balanced for energy-corrected
milk yield (ECM), days in milk, and
parity. Average days in milk and ECM
were 114 ± 56 d and 31.2 ± 3.4 kg/d in
1996 and 188 ± 30 d and 26.9 ± 4.6
kg/d in 1997. Primiparous cows (eight
in 1996 and four in 1997) were
equally distributed among blocks.
During a 2-wk preliminary period, all
cows were fed concentrate at the rate
of 1 kg for each 5 kg ECM. At the
conclusion of the preliminary period,
each block of cows was assigned
randomly to one of four grain to
milk ratios (0, 1:7, 1:5 or 1 kg concentrate for each 3 kg concentrate). A
commercial concentrate (ConAgra,
1996
Concentrate
1997
1996
Avg.
SD
Avg.
SD
DM
22.51
3.65
23.46
CP
ADF
NDF
IVDMD
Ash
Ca
P
Mg
K
18.49
21.47
49.14
70.27
10.27
0.58
0.49
0.22
2.82
1.73
0.90
1.86
6.10
0.82
0.06
0.03
0.02
0.32
14.61
25.22
51.57
67.34
10.75
0.52
0.36
0.18
2.57
Avg.
1997
SD
Avg.
SD
2.49
95.59
(% of DM)
0.29
92.61
0.30
2.93
17.30
2.67
9.51
3.64
29.25
8.34
73.77
2.07
8.01
0.06
1.66
0.05
0.79
0.01
0.38
0.37
0.95
(Mcal/kg)
0.65
0.66
1.08
1.80
0.33
0.11
0.03
0.02
0.05
17.88
17.69
43.02
77.35
9.66
1.92
0.99
0.40
1.07
0.23
3.87
0.65
1.05
0.03
0.06
0.08
0.01
0.02
(%)
Decatur, AL) was individually fed
twice daily during milking based on
the average ECM of each block. Any
concentrate refused was collected and
weighed. The amount of concentrate
offered was adjusted each week for
the average ECM of each block.
Samples of concentrate were collected
weekly for chemical analysis as
described previously. Milk yield was
recorded at each milking using
electronic milk meters (Westfalia, Elk
Grove Village, IL). Samples of milk
were collected at two consecutive
milkings each week for analysis of
percentage fat, protein, lactose, and
solids-not-fat (SNF, Tennessee DHI
Lab Services, Powell, TN) using a
Bentley 2000 (Bentley Instrument,
Chaska, MN) equipped with an A
filter. Water and portable shade
structures were available to cows at all
times. Body weight was measured on
2 consecutive d at the beginning and
end of the trial.
Analysis of covariance was conducted as a randomized block using
Proc Mixed procedures of SAS (16).
Cow within treatment was treated as
a random effect and week as a
repeated measure. Data within each
year were analyzed according to the
following model:
Yijk = + Ti + Wj + (T × W)ij +eijk
where Yijk = dependant variable; =
overall mean of the population; Ti =
effect of treatment i; Wj = effect of
week j; eijk = residual error. Linear and
quadratic contrasts of treatment were
included for level of concentrate.
Significance was declared at P<0.05
unless otherwise noted. Stepwise
regression analysis was conducted on
treatment means to determine the
effect of concentrate supplementation on milk yield and percentage
milk fat (17). Regression equations
for milk yield and percentage milk fat
were used to calculate the income
over concentrate cost over a range of
milk and concentrate prices.
Results and Discussion
Chemical composition of pasture
and concentrate is presented in Table
1. Pasture quality was higher in 1996
compared with 1997 because of
higher concentrations of CP and NEl,
higher IVDMD, and lower concentrations of ADF and NDF. The fertilization and pasture management was
similar in both years, so differences
in nutrient content are most likely
due to differences in the growing
166
Bernard and Carlisle
TABLE 2. Effect of level of concentrate on production of cows grazing
pasture.
Grain:milk ratio
Item
0
1:7
1:5
Contrast
1:3
SE
Linear
Quadratic
P
Concentrate
intake, kg/d
1996
1997
Milk, kg/d
1996
1997
Fat, %
1996
1997
Fat, kg/d
1996
1997
Protein, %
1996
1997
Protein, kg/d
1996
1997
Lactose, %
1996
1997
Lactose, kg/d
1996
1997
SNF, %
1996
1997
SNF, kg/d
1996
1997
ECMa, kg/d
1996
1997
Change in
BW, kg/d
1996
1997
aECM
0.0
0.0
4.1
4.4
6.2
6.1
8.7
10.5
0.0
0.3
0.0001
0.0001
0.0001
NS
21.4
19.8
27.2
24.4
29.1
28.8
31.5
30.4
1.7
1.5
0.0015
0.0006
NS
NS
3.04
3.60
3.03
2.87
3.13
2.61
2.97
2.61
0.13
0.25
NS
0.03
NS
NS
0.65
0.71
0.82
0.70
0.91
0.75
0.94
0.79
0.04
0.06
0.0002
NS
0.07
NS
2.71
3.02
2.92
2.98
2.97
3.07
2.73
3.11
0.07
0.14
NS
NS
0.01
NS
0.58
0.60
0.79
0.73
0.86
0.88
0.86
0.95
0.05
0.05
0.004
0.0001
0.07
NS
4.67
4.31
4.69
4.02
4.59
4.32
4.60
4.41
0.15
0.13
NS
NS
NS
NS
1.00
0.85
1.28
0.98
1.34
1.24
1.45
1.34
0.08
0.08
0.004
0.001
NS
NS
7.76
7.93
8.28
7.57
8.17
8.01
7.98
8.16
0.13
0.17
NS
NS
0.02
NS
1.66
1.57
2.25
1.85
2.38
2.31
2.52
2.48
0.12
0.12
0.0005
0.003
0.08
NS
19.4
19.8
24.9
22.1
27.2
25.2
28.4
26.7
1.2
1.4
0.0004
0.004
0.10
NS
-0.48
-0.08
-0.05
-0.10
-0.14
0.70
-0.09
0.99
0.39
0.23
NS
0.0015
NS
NS
= Energy-corrected milk (19).
season. The 1997 growing season was
wetter and cooler than 1996. The
average pre- and postgrazing herbage
mass and days on each paddock were
830 ± 410 kg/ha, 228 ± 113 kg/ha, and
1.4 d in 1996 and 1843 ± 761 kg/ha,
1169 ± 487 kg/ha, and 1.8 d in 1997.
The fiber and mineral content of
the concentrate (Table 1) was higher
in 1997 than in 1996. The higher
fiber content is presumably due to
greater inclusion of high-fiber byproducts in the concentrate in 1997
than in 1996. The reason for the
increase in mineral content in 1997 is
not known. Concentrate intake (CI)
increased quadratically (P<0.0001) in
1996 and linearly (P<0.0001) in 1997
(Table 2) according to the experimental design and to differences in initial
ECM yield among blocks.
Milk yield and composition are
presented in Table 2. Milk yield
increased linearly in 1996 (P<0.002)
and 1997 (P<0.0006) as the amount
of concentrate fed increased. Percentage milk fat was not affected by level
of concentrate feeding in 1996, but
decreased linearly (P<0.03) as the
amount of concentrate fed increased
in 1997. Yield of milk fat exhibited a
quadratic response (P<0.07) in 1996
due to a large increase as CI increased
from 0 to 1:5 and a small increase as
the amount of concentrate fed
increased from 1:5 to 1:3. Yield of
milk fat was not different among
treatments in 1997. Milk protein
percentage (P<0.07) and yield (P<0.01)
increased as the amount of concentrate fed increased from 0 to 1:5 but
declined or remained the same when
concentrate feeding increased from
1:5 to 1:3 in 1996. Milk protein
percentage was not different in 1997,
but yield increased linearly (P<0.0001)
as the amount of concentrate fed
increased. There were no differences
in milk lactose percentage or yield in
either year. Percentage (P<0.02) and
yield (P<0.08) of SNF exhibited a
quadratic response in 1996 similar to
that described for milk protein.
Percentage SNF was not different in
1997, but yield increased linearly
(P<0.003) with increased concentrate
feeding in 1997. Yield of ECM increased linearly in both years and
tended to exhibit a quadratic response (P<0.10) in 1996 because of
the reduced increase in yield as the
amount of concentrate fed increased
from 1:5 to 1:3.
Polan et al. (13) reported increased
milk yield and decreased percentage
milk fat when the amount of a cornmineral concentrate fed increased
from 3.6 to 7.3 kg/d for cows grazing
orchardgrass, fescue, and Kentucky
bluegrass pasture. In contrast,
Hoffman et al. (8), Jones-Endsley et
al. (9), and Salinas et al. (15) did not
observe any difference in milk yield
for cows grazing predominately
167
Concentrate Feeding with Pasture
was similar at all milk prices, but the
optimum varied (Figure 2). In general, as concentrate price increased,
the level of CI at which income over
concentrate cost was optimized
decreased. But, as milk price increased, the level of CI at which
income over concentrate cost was
optimized increased. The effect of
increasing concentrate cost was less
apparent at higher milk prices than
at lower milk prices. For example,
when milk was priced at $12/45.4 kg,
income over concentrate cost was
optimized at 6 kg CI when concentrate cost was $170/907 kg, but the
optimum CI was 4 kg when concentrate cost was $250/907 kg. When
milk was priced at $18/45.4 kg,
income over concentrate cost was
optimized at 7 kg CI when concentrate cost were $170/907 kg and 6 kg
when concentrate cost was $250/907
kg.
Figure 1. Effect of concentrate intake (CI) on
milk yield (A) and milk fat percentage (B) of
Holstein cows grazing annual ryegrassCrimson clover pasture.
orchardgrass pastures and fed varying
rates of concentrate.
Regression analysis of the effects
of CI on milk yield resulted in the
following equation:
milk yield (kilograms per day) = 20.4
+ 1.598 CI –0 .0011 CI3
(R2=0.94; P=0.001, Figure 1A). The
intercept of 20.4 kg milk is similar to
that reported by Conrad and Keuren
(5). The cubic effect of CI on milk
production indicates a diminishing
response to concentrate as greater
amounts are fed. The effect of CI on
milk fat percent was linear: milk fat,
percentage = 3.268-0.27 CI (R2 = 0.46,
P<0.10, Figure 1B).
Effect of CI on herbage intake was
estimated using NRC (12) NEl requirements for maintenance, milk yield,
and BW change and NEl intake from
concentrate. Estimated herbage
intake in 1996 decreased (11.1, 10.4,
9.0, and 7.2 kg/d for 0, 1:7, 1:5, and
1:3, respectively) as the amount of
concentrate fed increased. A similar
response was calculated for 1997:
13.0, 9.2, 11.4, and 8.9 kg/d for 0, 1:7,
1:5, and 1:3, respectively. These data
suggest that concentrate replaced
forage at the higher rates of concen-
Figure 2. Effect of concentrate intake and
milk price on income over concentrate cost
when concentrate cost $175 (A) or $250 (B)
per 907 kg.
Implications
Feeding high levels of concentrate
when high quality pasture is readily
available increases milk yield, but the
response diminishes as additional
concentrate is fed. The optimum level
trate feeding. Meijs and Hoekstra (11) of concentrate feeding that optimizes
reported that herbage OM intake
income over concentrate cost is a
decreased as the amount of concenfunction of milk price and concentrate fed increased when herbage
trate cost. The relative differences in
mass was high, but herbage OM
income over concentrate cost obintake was not affected by the
served in this trial do not take into
amount of concentrate fed when
consideration forage cost, forage
herbage mass was low.
intake, or long-term effects of BW
Change in BW (kilograms per day) change, which must be considered.
was not different among treatments
However, these data indicate an
in 1996, but BW increased linearly
opportunity for dairy producers to
(P<0.002) with increasing CI in 1997. reduce CI and maintain milk yield
Crude protein content of pasture was periods when high quality pasture is
lower in 1997 than in 1996, which
readily available.
may have resulted in a deficiency of
metabolizable protein or essential
amino acids so that the extra energy
from the concentrate was used more
The authors thank Hugh
efficiently for BW gain rather than
Moorehead, David Plunk, Jason
for milk synthesis.
Goad, and the staff of Ames PlantaIncome over concentrate cost was
tion for care of animals and colleccalculated over a range of milk ($12
tion of samples and to Eddie Jarboe
to $18/45.4 kg) and concentrate ($175 and staff of the Animal Science
to $250/907 kg) prices. The income
Laboratories for assistance with
over concentrate cost response curve
sample analysis. The research in-
Acknowledgments
168
Bernard and Carlisle
cluded in this report was partially
funded by the Hobart Ames Foundation under the terms of the will of
the late Julia Colony Ames.
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