Effects of Heterosis on Reproduction in Hereford, Angus and Shorthorn Cattle2

Effects of heterosis on reproduction were evaluated in a comprehensive experiment comparing straightbred Hereford (H), Angus (A) and Shorthorn (S) females to reciprocal cross females among these breeds when mated to produce crossbred calves with equal additive and non-additive genetic composition. This phase of the experiment involved 570 matings (cow-years) of straightbred cows and 687 matings of crossbred cows accumulated over six breeding seasons, 1962 through 1967. 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 the effects of heterosis expressed from 2 through 6 years of age and 3 through 8 years of age in each management regime, respectively. Analyses over all breeds, ages and systems of management revealed that the effects of heterosis significantly (P<.05) reduced the interval from parturition to first estrus and the average date of conception. Calf crop weaned was 6.4% greater for crossbred than for straightbred cows (P<.01).