New Zealand Journal of Agricultural Research abstracts
Some relationships between weights of growing heifers and their subsequent
lactation performances
E. H. van der WAAIJ
P. J. B. GALESLOOT
D. J. GARRICK
Department of Animal Science
Massey University
Palmerston North, New Zealand
Abstract Studies have shown that rearing regimes that result
in heifers of heavier liveweights give rise to greater subsequent lactation
yields than those regimes resulting in heifers of average liveweight. Rearing
heifers to heavier weights is more costly because of additional management
inputs and reduced pasture utilisation. The objective of this research was to
quantify some relationships between immature weights and subsequent milk yields
and compositions in each of the first three lactations. Genetic and phenotypic
correlations between liveweights at 9, 15, and 21 months of age (LW9, LW15,
LW21) and lactation yields were obtained from records on 2365 mixed breed dairy
cows. Genetic correlations between first lactation yields of milk, fat, and
protein (MY1, FY1, PY1) and liveweights were all positive and ranged from 0.14
(LW9 and FY1) to 0.45 (LW15 and PY1). Genetic correlations between weights and
milk and fat yields tended to be slightly lower at second and third lactations
as compared to first lactation, but were associated with high standard errors.
LW15 had the highest genetic correlations with yield traits for the three
lactations. Phenotypic correlations between liveweights and yields were of
similar size to the genetic correlations. The effects of rearing management
were estimated from regressing average lactation yields of groups of
contemporary cows in subsequent years on average liveweights of the same groups
as immature heifers. Average weights and yields were adjusted for differences
in genetic merit between groups before regression analysis. Management that
resulted in a 1 kg increase in LW15 caused a 6.7 litre increase in MY1, 0.27 kg
increase in FY1, and 0.18 kg increase in PY1. Profit per lactation was
estimated to increase by $0.48 per kg increase in immature weight.
Keywords immature liveweight; lactation yields; dairy
cattle
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 87-92
0028-8233/97/4001-0087 $2.50/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (480K); (scanned from paper original: notes about this process)
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