The aims of the present study were to estimate genetic parameters, as well as phenotypic, genetic and environmental trends for age at first calving (AFC) and calving intervals (CI) on Gyr dairy breed, using a multivariate derivative-free restricted maximum likelihood (MTDFREML) with an animal model. The mathematic model for calving interval included herd-year of calving, calving season, and the covariate age of cow as fixed effects, and animal, and permanent environment as random effects. The model for age at first calving included herd-year of birth and season of birth as fixed effects, and animal as random effect. Through the bivariate analyses, estimates of heritability were: for age at first calving 0.17 and for calving interval 0.06. The estimate of repeatability for calving interval was 0.17. The phenotypic, genetic and environmental correlations between age at first calving and calving interval were 0.06, 0.37 and 0.03, respectively. The phenotypic, genetic and environment annual trends for age at first calving were, respectively, -0.446±0,077 (P<0.01), 0.008±.013 and -0.454 months based on breeding values of cows, and -0.185±0.083 (P<0.05), 0.051±0.059 and -0.236 months based on breeding values of bulls. The phenotypic, genetic and environment annual trends for calving interval were, respectively, -1.25±0.95, -0.98±0.19(P<0.01) and -0,27 days based on breeding values of cows, and -0.88±1.07, -1.62±0.40 (P<0.01) and 0,74 days based on breeding values of bulls.
Cattle; dairy Gyr; genetic parameters; phenotypic trend; genetic trend
