Estimated genetic parameters for mature cow live weights during lactation in a multi-breed dairy cattle population

Live weight (LWT) is an important trait for dairy production systems as it influences both maintenance feed requirements and beef revenue from culled cows and from offspring surplus to replacements. The breeding goal for the New Zealand dairy industry includes LWT. This study estimated genetic parameters for LWT during lactation from some animals in the New Zealand multi-breed dairy cattle population. A total of 31,922 LWT records from 11,222 lactating dairy cattle born from 1988 to 2015 were used for the analysis. Estimation of (co)variance components used Gibbs sampling from pedigree-based models. The posterior mean heritability estimates using scale weights were consistently high across six lactations and ranged from 0.57 to 0.64. There were high genetic correlations between the scale weights measured during different lactations (>0.95). We further estimated the posterior mean heritability for subjective liveweight scores recorded from first lactation using trained inspectors and the estimate was 0.36, lower than those heritability estimates from scaled weight. Further, the genetic correlations between subjective liveweight score and scale weights at various lactations ranged from 0.91-0.92. It is recommended that only scale weights be used for national genetic evaluation.