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Data on Angus (ANG), Charolais (CHR), Hereford (HER) and Limousin (LIM) cattle were used to estimate genetic parameters for calving difficulty (CD) and to quantify genetic relationships among CD, birth weight (BWT) and gestation length (GL). Bayesian analysis was carried out using Gibbs sampling to obtain means of marginal posterior distributions. Estimated heritabilities for direct genetic effect of CD were 0.24, 0.22, 0.31 and 0.22 for ANG, CHR, HER and LIM, respectively while maternal heritabilities ranged from 0.13 to 0.20. Genetic correlations between direct genetic effects of CD with BWT were highly positive and with GL were moderately positive for all four breeds. Low to moderate negative correlations of maternal genetic effect of CD with direct genetic effects for BWT and GL were estimated. This study showed that CD was moderately heritable in all four breeds and therefore, genetic progress is possible through selection. The ANG and HER had similar genetic correlations. Among the four breeds, LIM had slightly higher direct and maternal genetic correlation for CD and higher correlations between the maternal genetic effects of all three traits. However, moderate to high positive correlation between direct genetic effects of CD, BWT and GL show selection for lower BWT and GL would decrease CD in all four breeds. |
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