932
Estimation of Genetic Parameters for Reproductive Traits in a Multibreed Population of Beef Cattle
Reproductive traits are very important economically relevant traits in beef cattle production, and estimation of genetic parameters for these traits is necessary to optimize selection response and improve profitability of beef production. The objective of this research was to determine genetic parameters for the reproductive traits of heifer pregnancy (HPG), stayability (ST), rebreeding rate (RR) and calving ease (CE) in a multi-breed cattle population. We analyzed a dataset of 10,245 HPG and ST records, 8,740 RR records and 11,779 CE records from a large commercial operation in Nebraska that included pedigree information, contemporary groups and sire breed. Hierarchical threshold mixed models based on a probit link specification were used for the bivariate analysis of HPG and ST records and for the univariate analysis of RR and CE with maternal records. The posterior means and 95% posterior probability intervals of additive variance were estimated to be 0.227±0.103 [0.104, 0.418] for HPG and 0.123±0.043 [0.049, 0.215] for ST, and 0.211±0.101 [0.074, 0.449] for RR and 0.216±0.147 [0.04, 0.549] for CE, respectively. Also, the posterior mean and 95% posterior probability interval (PPI) of direct maternal variance were estimated to be 0.702± 0.229 [0.355, 1.230] for CE. Posterior mean inferences on direct heritability were found to be 0.056±0.019 [0.025, 0.099] for HPG and 0.065±0.021 [0.028, 0.111] for ST, 0.138±0.053 [0.056, 0.254] for RR and 0.08±0.05 for CE, respectively. Posterior mean inferences on maternal heritability were found to be 0.263±0.07 [0.145, 0.417] for CE. The posterior mean of genetic correlation between HPG and ST was low and negative (-0.174±0.289) and insignificant with [-0.665, 0.353] of 95% PPI. The posterior mean and 95% PPI of direct maternal genetic correlation was -0.235±0.132 [-0.509, 0.024] for CE. The low heritability values observed in this study are similar to literature values and the low and negative correlation between HPG and ST indicate that genetic improvement geared towards improving HPG may have antagonistic effect on ST but this effect is not statistically significant.
Keywords: Reproductive traits, genetic parameters, threshold model