Abstract
Two experiments of 5-weeks duration, using Friesian cows, were conducted at
the Kyabram Dairy Centre during September–October (experiment 1) and
November–December (experiment 2), 1998. The aim of the research was to
determine whether the level of substitution with the feeding of concentrates
to grazing dairy cows would be increased by thinner body condition (3.4
v. 5.2 units) and by larger body size (618
v. 486 kg) because both these factors would be expected
to increase the level of unsupplemented pasture intake. In both experiments,
there were 2 pasture allowances (targets of 25 and 50 kg DM/cow. day) and
2 weeks of supplement (0 and 5 kg DM/cow. day).
In experiment 1, pasture intake increased significantly
(P<0.05) with the increase in pasture allowance and
decreased with supplementation. Levels of substitution averaged 0.56 and 0.47
kg DM/kg DM when concentrates were fed to cows with low and high body
condition, respectively. However, variation in the data meant that body
condition did not have a significant (P>0.05)
influence on the positive relationship between substitution and unsupplemented
pasture intake. The only effects of body condition on animal production were
that the high body condition cows produced milk with a higher fat content, and
they lost more body condition, than the low body condition cows
(P<0.05). The increase in pasture allowance
significantly (P<0.05) increased milk production and
milk urea content, and decreased the loss in body condition. Feeding
concentrates significantly (P<0.05) increased milk
production and prevented any losses in body condition, but milk urea content
declined with supplementation.
In experiment 2, heavy cows ate more pasture than light cows
(P<0.05), and increasing the pasture allowance
increased pasture intake while providing cows with concentrates reduced
pasture intake (P<0.05). When substitution was
considered relative to unsupplemented pasture intake (kg DM/cow.day),
light cows exhibited significantly (P<0.05) more
substitution than heavy cows, but when pasture intake was expressed as a
percentage of liveweight, there were no significant (P>0.05) differences in
substitution between light and heavy cows at common intakes. Heavy cows
produced more (P<0.05) milk with a lower protein content than light cows.
Increasing the pasture allowance and supplementation with concentrates both
significantly (P<0.05) increased milk production and milk protein content,
while the higher pasture allowance reduced body condition loss and
supplementation increased (P<0.05) liveweight. Feed conversion efficiencies
were the same for light and heavy cows, at 1.68 kg FCM/kg DM of total
intake in both cases. The hypothesis that substitution would increase as
intake increased was supported by the results obtained for both body condition
and body size, since body condition affected neither intake nor substitution
while liveweight influenced both.
Subject
General Agricultural and Biological Sciences
Cited by
19 articles.
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