Effects of Heterosis on Age and Weight at Puberty in Beef Heifers

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Abstract
The Hereford, Angus and Shorthorn breeds and all reciprocal crosses among them were included in an experiment that was designed to evaluate heterosis effects in crosses among these breeds. The traits evaluated were age at puberty, weight at puberty, age at puberty adjusted for average daily gain from birth to weaning (200 days) and age at puberty adjusted for average daily gain from weaning to 396 days. Data are presented and discussed for these traits on 182 heifers from 2 calf crops developed to produce their 1st calves as 3-year-olds (low wintering level) and 171 heifers from 2 calf crops developed to produce their 1st calves as 2-year-olds (high wintering level). Preweaning average daily gain had a significant effect on age at puberty in both management groups, while the effect of postweaning average daily gain was significant only at the low wintering level. Significant (P < .01) heterosis effects existed for age at puberty. After age at puberty was adjusted for the effects of average daily gain from birth to weaning and average daily gain from weaning to 396 days, 1/2 to 3/4 of the heterosis effect on age at puberty was still present. Thus, there was a significant (P < .01) heterosis effect on age at puberty independent of heterosis effects on average daily gain. From these results it is concluded that there is a heterosis effect on age at puberty in addition to that exerted through average daily gain. Heterosis effects on age and weight at puberty were greatest for the Hereford X Shorthorn and the reciprocal cross. This was consistent for both management groups of heifers.