The objective of this study was to estimate genetic parameters for milk yields, milk concentrations and ratios of milk components. Herd-test records from 268 Jersey cows from a Waikato dairy farm were obtained along with pedigree information. Genetic and phenotypic (co)variances for daily yields of milk (MY), fat (FY), protein (PY), milksolids (MSY; FY + PY) and lactose (LY), percentages of fat, protein, and lactose, and ratios of protein to fat (P:F) and protein to protein plus lactose (P:PL), and somatic cell score, were obtained with single trait and bivariate animal models using a restricted maximum likelihood methodology. The models included the fixed effects of month of calving and days in milk, modelled using an exponential curve, lactation number and the random effects of animal and cow permanent environment effects were also included in the model. Heritability estimates were 0.50 ± 0.12 (standard error) for MY, 0.25 ± 0.10 for FY, 0.30 ± 0.12 for PY, 0.27 ± 0.11 for MSY, 0.50 ± 0.12 for LY, 0.24 ± 0.04 for P:F ratio and 0.53 ± 0.04 for P:PL ratio. The genetic correlations for daily yields were high and positive. The genetic correlation between MSY and P:F ratio was -0.35 indicating that increases in MSY under the current breeding objective will decrease the P:F ratio, thus departing from an optimal ratio for whole milk powder processing.
Proceedings of the New Zealand Society of Animal Production, Volume 72, Christchurch, 76-80, 2012
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