Determining the utility of adolescent live weight data to predict two-year-old live weight in New Zealand dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science, Master of Science in Animal Breeding and Genetics at Massey University, A L Rae Centre for Animal Breeding and Genetics, Waikato, New Zealand

Abstract

The purpose of this research was to establish the utility of adolescent live weight data measured across cohorts of growing animals for predicting live weight in first lactation. Live weight is associated with the growth and maintenance feed requirements of a cow. Selection that simultaneously takes account of milk income and feed requirements of dairy cattle can increase future farm profitability. Estimated breeding values (EBVs) for mature cow live weight are currently predicted using Live weight phenotypes measured during lactation. Breeding companies in NZ actively measure the first lactation live weight of a small proportion of the nation’s dairy cows—the daughters of their bulls—to improve their ability to identify superior bulls. Accurate EBVs obtained at an earlier age can allow reliable selection of superior young bulls which would shorten the generation interval, increasing the rate of genetic progress. The purpose of this research was to determine the utility of adolescent live weight (i.e. live weight prior to first lactation) for predicting variation in live weight measured in first lactation. We completed two studies. In the first study (Section 4), we produced the (co)variance parameters for live weights measured at four ages, from six months old through to first lactation. Our hypothesis for this study was that live weight measured through adolescence would share a strong positive genetic relationship with live weight measured during lactation. Our results support this hypothesis, as estimates of genetic correlations between weights at different ages ranged from 0.79 to 0.97. In the second study (Section 5), we produced live weight EBVs using live weight measured though adolescence. For comparison, we produced EBVs using just live weight measured during first lactation. Our hypothesis was that the accuracy of the live weight EBVs would be improved by including adolescent live weight. Our results showed that including adolescent live weight phenotypes improved the accuracy of the live weight EBVs for animals with adolescent live weights, and their progeny. We concluded that adolescent live weights are a useful predictor of live weight later in life, and should be incorporated as a predictor trait for the national live weight EBV in NZ.