The effect of age, weight and sire on pregnancy rate in cattle

The goal was to estimate the heritabilities and genetic variances for pregnancy rate (PR) and calving date (CD) in cattle along with the effect of weight, age and sire on PR and CD. The data consisted of 4,999 records on PR and CD. Statistical models for included year and herd as fixed effects, premating/postmating weight and age as covariates, and sire of embryo, maternal grandsire (MGS) and permanent maternal environmental effects as random effects. Direct and maternal effects on PR/CD were estimated using sire-MGS and animal models in REML. PR independent of the culling strategy increased significantly from age 2-6 and decreased significantly from age 6-11 (P < 0.01). There was a significant quadratic effect of premating cow weight on PR, with lower PR for low weights (P < 0.01). Overall, cows with a pre-mating weight of 550 kg had the greatest PR. There was also a significant linear effect of the gain in weight between premating and weaning on PR with lower PR for cows that lost weight over mating (P < 0.01). The maternal additive heritability was 0.001 ± 0.012 and the direct additive heritability for PR was 0.024 ± 0.020.