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
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Date
2019
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Massey University
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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.
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Keywords
Dairy cattle, New Zealand, Weight, Heifers, Breeding