Variance components and genetic parameters for early growth traits in a mixed population of purebred Bos indicus and crossbred cattle

Variance components and direct and maternal heritabilities were estimated for weight at birth ( n =4960), weaning at 180 days ( n =4250) and yearling at 365 days ( n =3330) and preweaning average daily gain ( n =4250). Data were from calves of purebred ( Bos indicus ) Boran, Barca and Horro and their crosses with Friesian, Jersey and Simmental breeds that were separated from their dams 1 day after birth and fed milk from a bucket. Data were analysed using six alternative animal models (direct and including or excluding maternal associated effects). Direct heritability estimates from the best model for each trait were: 0.14±0.03 for birth weight, 0.08±0.03 for weaning weight, 0.06±0.02 for preweaning average daily gain and 0.13±0.03 for yearling weight. Direct maternal heritability estimates were small and significantly different from zero for only birth weight (0.07±0.02), weaning weight (0.04±0.02) and preweaning average daily gain (0.04±0.02). Direct genetic correlations between birth weight and the other three traits were: 0.66±0.08, 0.55±0.19, 0.50±0.12 with weaning weight, preweaning average daily gain and yearling weight, respectively. The genetic correlation between weaning weight, preweaning average daily gain and yearling weight was high and ranged from 0.82±0.11 to 0.97±0.01. Small, but nonzero maternal heritabilities estimated for weaning and preweaning average daily gain for artificially reared calves in this study should be interpreted cautiously because of the potential bias from unaccounted breed additive and nonadditive effects in the dam. Results of this study also showed that estimates of variance components and genetic parameters suitable for general use can be obtained from mixed purebred and crossbred data after appropriately accounting for breed additive and nonadditive effects.