Postweaning growth and reproduction characteristics of heifers sired by bulls of seven breeds and raised on different levels of nutrition

Heifers produced from sires of seven breeds (Hereford, Angus, Belgian Blue, Piedmontese, Brahman, Boran, and Tuli) and Angus, Hereford, and MARC III (four-breed composite) cows were evaluated. Weaned heifers were placed in three treatment groups of moderate nutrition (15.8 Mcal ME/d), 80% of moderate nutrition (12.6 Mcal ME/d), or fed as a mixed-breed group (16.3 Mcal ME/d). Average daily gain (ADG) from 228 d of age through breeding was measured. There was a sire breed x group interaction (P < .0001) for ADG in the drylot. Sire breeds differed in their 365-d BW (P < .0001), and 365-d BW of heifers in the low group (315 [+ or -] 4 kg) were lighter (P < .0001) than those of heifers in the high group (346 [+ or -] 4 kg). During breeding, heifers that had been in the low group in the drylot had a higher ADG (.58 [+ or -] .02 kg/d) than heifers in the high group (.39 [+ or -] .03 kg/d). Age of heifers at puberty did not differ (P = .06) between the low (362 [+ or -] 5 d) and high groups (357 [+ or -] 5 d). Heifers from MARC III (358 [+ or -] 5 d) and Angus (358 [+ or -] 6 d) dams reached puberty at a younger age than did heifers with Hereford dams (380 [+ or -] 9 d). Age at which puberty was expressed differed with sire breed (P < .001). The proportion of heifers that were pregnant at palpation (.90) did not differ between sire breeds (P = .24), dam breeds (P = .40), or group (P = .56). Breed differences in postweaning ADG and in the manner in which the population expresses puberty allow for selection of breed types that will optimize cow herd performance. Key Words: Beef Cattle, Heifers, Puberty, Pregnancy