Keith E. Gregory

Characterization of Biological Types of Cattle IV. Postweaning Growth and Puberty of Heifers

Postweaning growth and puberty traits were studied in 965 heifers produced by mating Hereford and Angus cows to Hereford, Angus, Jersey, South Devon, Limousin, Charolais and Simmental sires. Estrus was checked twice daily from 250 to either 480 or 510 days of age and age and weight at puberty were evaluated. Puberty was defined as date of first standing estrus. Charolais, Simmental and South Devon crosses were the heaviest at 400 days of age followed closely by Hereford-Angus and Limousin crosses with Jersey crosses the lightest. Jersey crosses were 16% lighter than Charolais and 8.7% lighter than Limousin crosses at 400 days of age. For percentage of heifers reaching puberty at each 30-day period from 300 to 450 days of age, breed crosses separated into three distinct groups. A higher percentage of Jersey crosses and a lower percentage of Charolais and Limousin crosses reached puberty with HerefordAngus, South Devon and Simmental crosses intermediate throughout this age range. Breed crosses divided into the same three groups on the basis of average age at puberty. Charolais crosses were heaviest at puberty, followed by Limousin and Simmental, then South Devon and Hereford-Angus, with Jersey crosses the lightest. Heifers from Angus dams were 26 days younger and 9 kg lighter at puberty than those from Hereford dams. Heterosis in HerefordAngus reciprocal crosses for age at puberty was 19.5 days with no effect on weight at puberty. (