Some relationships between weights of growing heifers and their subsequent lactation performances

摘要

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 lac...