Genetic parameters and relationships between heifers rebreeding and hip height in Nellore cattle
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The objective of this study was to estimate heritability and verify the genetic correlations between heifers subsequent rebreeding with weaning hip height (WHH) and yearling hip height (YHH), using Bayesian inference. The (co)variance components and genetic parameters were estimated using an animal nonlinear (threshold) model for subsequent rebreeding and an animal linear model for WHH and YHH. The animal model included the contemporary group as the systematic effect and direct additive genetic and residual effects as random effects. Genetic maternal and maternal permanent environment effects were also considered in the model for WHH. Covariables considered were: rest period (linear effect), for subsequent rebreeding; animal age at measurement and age of cow at calving (linear and quadratic effects), for WHH and YHH. Direct heritability estimates were 0.14±0.04, 0.45±0.03 and 0.51±0.02 for subsequent rebreeding, WHH and YHH, respectively. For maternal effects, the heritability of WHH and the proportion attributed to the permanent environmental effect were 0.08±0.02 and 0.04, respectively. The posterior means of genetic correlations estimates between subsequent rebreeding with WHH and YHH were -0.16±0.05 and -0.21±0.04, respectively. Selection response for subsequent rebreeding of heifers would be low. Increase in the rate of subsequent rebreeding could be obtained with improvements in the management applied to heifers. The inclusion of hip height in selection indices, especially when measured at yearling, promotes small reduction in the rate of subsequent rebreeding of Nellore heifers.