Characterization of cattle of a five-breed diallel. III. Puberty in bulls and heifers.

Abstract

Pubertal characters of bulls and heifers produced in a diallel mating of Angus, Brahman, Hereford, Holstein and Jersey cattle were analyzed. Ninety-one heifers and 138 bulls in individual pens adn 286 bulls in drylots were fed a 72% TDN diet ad libitum; another 384 heifers were placed on pasture with supplemental feed. Puberty in heifers was defined as time of first ovulatory estrus; in bulls, as first detection of sperm cells in an electroejaculate. Breed type least-squares means, adjusted for birth month, were estimated within sex-nutrition-management groups and then decomposed into breed effects, average heterosis (h), general combining ability (GCA) and specific combining ability (SCA) by diallel analysis techniques. Breed effects were a significant source of variation for all characters studied. Heterosis (h, GCA, SCA) was not significant for pubertal age of bulls or heifers receiving complete diets in pens, a rather high nutritional plane. However, on pasture, crossbred heifers reached puberty at a younger age (P less than .05) than straightbreds. Average heterosis was significant (P less than .05) for increased weight and hip height at puberty and ratios involving these characters for both sexes. Specific combining abilities were not statistically significant for the majority of the pubertal characters, yet large differences among estimates of combining abilities were expressed. Ad libitum feeding of the penned heifers tended to decrease pubertal age and increase pubertal size as compared to pubertal age and size of pastured heifers. The breed type x management interactions within both sexes indicated a different ranking of the breed types for each management regimen.