Direct and maternal effects on preweaning characters of Brahman, Hereford and Brahman-Hereford crossbred cattle

Abstract

Birth weight, preweaning gain, and weaning weight (adjusted 180-day weight) data, collected at McGregor, Texas were analyzed to evaluate genetic differences. Preweaning gain was calculated as adjusted 180-day weight less birth weight. All statistical models included the effects of dam age, year, season and sex. Model I was a breedtype model. Model II redefined breedtype as direct additive, direct heterotic, maternal additive and maternal heterotic effects. Model III was a breedtype model including breedtype interactions with other effects in the model. Model IV was Model II plus tests of heterogeneity of genetic effects across classes of other effects in the model. Brahman dams produced calves with lighter birth weights while Brahman sired calves were heavier at birth than those by other sire breedtypes. The estimated Brahman direct additive effect on birth weight was 4.6 kg greater than Hereford. The Brahman maternal additive effect was 7.5 kg less than Hereford. The Brahman direct additive effect on birth weight was 7.5 kg greater than Hereford for bulls and 2.3 kg greater than Hereford for heifers. The Brahman maternal effects on birth weight were 11.2 and 6.5 kg less than Hereford for bulls and heifers, respectively. Calves out of F(,1) dams had larger preweaning gains than those of other dam breedtypes. The Braham direct additive effect on preweaning gain was 17.7 kg less than Hereford and the Brahman maternal additive effect was 20 kg greater than that of Herefords. Direct and maternal heterotic effects on preweaning gain were 19.6 and 19.5 kg, respectively. The Brahman maternal additive advantage of preweaning gain was greatest for young dams. The Brahman maternal additive effect was greater than Hereford for spring and summer born calves but less than Herefords for fall calves. Results of weaning weight analyses were similar to preweaning gain analyses. The largest effects on weaning weight were direct and maternal heterosis which were 21.6 and 19.8 kg, respectively. Brahman maternal additive effects on weaning weight exceeded Hereford for 2-, 3- and 4-year-old dams, but Hereford maternal additive effects on weaning weight were greater than Brahman for 5- to 8-year-old dams.