Abstract
Effects of heterosis on milk production and maternal heterosis on preweaning growth traits and conformation score were evaluated in reciprocal crossbred and straightbred cows of Hereford (H), Angus (A) and Shorthorn (S) breeds. Maternal heterosis was estimated from the difference between progeny of crossbred and straightbred dams sired by the same bulls of a third breed. A total of 555 and 420 calves were produced by crossbred and straightbred dams, respectively. Milk production and composition were evaluated on a sample of 149 crossbred and 101 straightbred cows ranging from 2 to 5 years of age. Approximately one-half of the cows were developed and managed to calve first as 2-year-olds and one-half as 3-year-olds to evaluate effects of maternal heterosis expressed from 2 through 6 years of age and 3 through 8 years of age in each management regime, respectively. Over all breeds, ages and management regimes, effects of maternal heterosis were 1.7% for birth weight (P<.05), 3.6% for weight at 135 days (P<.01), 4.7% for weight at 200 days (P<.01) and one-sixth of a grade (P< .01) for conformation. These effects of maternal heterosis did reflect greater and more persistent milk production in favor of crossbred cows over straightbred cows by 0.9% at 2 weeks postpartum, 7.5% at 6 weeks postpartum (P<.05), 6.1% at about 14 weeks postpartum and 38% (P<.01) at weaning at about 29 weeks postpartum. Copyright © 1974. American Society of Animal Science. Copyright 1974 by American Society of Animal Science.