The objectives of this study were to estimate heritability for culling age (TPR), ages at first (IDPP), at second (IDSP) and at third calving (IDTP) and genetic correlations of these traits with adjusted and unadjusted weights for condition score, body size indexes and condition score at first mating, at first calving and at mature age. Variance and covariance components were estimated by REML using univariate and bivariate models including the fixed effect of contemporary group and additive direct genetic and residual as random effects. Heritability estimates obtained from univariate analyses were 0.10 ± 0.05 (IDPP), 0.08 ± 0.05 (IDSP), 0.14 ± 0.06 (IDTP) and 0.06 ± 0.00 (TPR) and indicate low response to selection on these traits. Genetic correlation estimates suggest that selection for increasing mature weight will reduce culling age but for heavier weight at first mating, at first calving and at maturity will not significantly change ages at first, at second and at third calving. Selection on body size indexes and on cow weights adjusted for condition score may result in similar correlated responses for reproductive traits and longevity which would be higher than those from selection on unadjusted cow weights.
age at calving; beef cattle; body weight; cow size; days in herd; genetic parameters
