Estimation of genetic parameters of calving ease in first and second parities of Canadian Holsteins using Bayesian methods

Abstract

Genetic parameters of calving ease in first and second parities of Canadian Holsteins were estimated using a Bayesian approach. Multiple-trait calving ease records on 94 925 cows (no missing records) were analyzed with a threshold model. The model included a fixed effect for sex of calf and random effects of herd–year–season, sire of cow, and sire of calf. Gibbs sampling was used to generate ten chains of 20 000 samples each, which were used to obtain posterior means for each parameter. Estimates of heritabilities were 0.26 and 0.17 for first and second lactations, respectively. Genetic correlations between lactations were 0.67, indicating that the scores were measures of distinct genetic traits. Direct heritabilities of 0.14 and 0.10 in first and second lactations, respectively, were approximately twice as large as the respective maternal heritabilities of 0.08 and 0.04. Estimates of genetic correlations among all combinations of direct and maternal genetic effects were positive, approximately 0.35, which conflicted with many previous studies. This positive correlation was confirmed by reanalyzing another sample of data with REML and by calculating correlations between official Canadian sire ETA for direct and maternal genetic effects on calving ease. Multiple trait genetic evaluation of calving ease should theoretically provide more precise predictions of breeding values than single-trait repeated records models.