Heterosis and Breed Effects in Preweaning Traits of Angus, Hereford and Reciprocal Cross Calves

Records on 1,661 Angus, Hereford and reciprocal cross calves were analyzed to examine effects of breed of sire, breed of dam, sex of calf, year-age of dam and heterosis on percent dystocia, peri- and postnatal survival and preweaning weights and growth rate. Breed of sire, breed of dam, sex of calf and year-age of dam were significant (P<.01) sources of variation for most of the preweaning characters examined.Calves by Hereford sires were 1.4 kg heavier at birth and experienced 9.3% more dystocia than calves by Angus sires. Angus-sired calves were 4.1 kg heavier at 200 days than Hereford-sired calves. There were no significant breed of sire effects for birth date or calf survival.Angus dams gave birth to calves 5.2 days earlier in the calving season with 9.5% fewer incidences of dystocia than Hereford dams. Calves from Angus cows were 1.7 kg lighter at birth and 14.9 kg heavier at 200 days.Male calves were heavier at birth and weaning and exhibited a higher incidence of dystocia and a lower survival rate than females. Three-year-old dams produced heavier calves at birth with less dystocia, with higher survival rates and heavier weaning weight than 2-yearold dams.Heterosis effects were observed for birth weight (3%) and preweaning growth (8%). However, there were no significant differences between straightbred and crossbred calves for percent dystocia or for peri- and postnatal survival. No significant differences between sexes were observed for amount of heterosis.