Preweaning Performance of Calves from Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano Sires Bred to Brangus Cows Managed on Native Rangeland or Improved Forages1, 2

Preweaning data on 511 spring-born calves from 187 Brangus cows and 129 Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano sires were measured over a 4-yr period to determine sire breed, sex, and age of dam differences under 2 preweaning forage environments: 1) native tallgrass rangeland (native) or 2) improved warm-season forages (improved). Sire breed differences in birth weight varied across forage (P < 0.05) with Romosinuano-sired calves on improved forages ranked intermediate in birth weight compared with other sire breeds but lightest on native forages. Calves from Charolais and Gelbvieh tended to be heavier at 205 d of age than calves from other sire breeds on improved forages (P < 0.05, except Gelbvieh vs. Hereford, P < 0.12) whereas on native forages, Bonsmara-, Charolais-, and Gelbvieh-sired calves were similar but were heavier than Brangus- and Romosi-nuano-sired calves (P < 0.10). Steer calves were heavier than heifer calves on improved forages (P < 0.01) but not on native forages. Sire breed differences were not significant on improved forages for weaning condition score. On native forage, weaning condition scores were greater for calves sired by Bonsmara and Hereford (P < 0.05) compared with Brangus-, Charolais-, and Gelbvieh-sired calves, and Charolais-sired calves were lesser than other sire breeds (P < 0.05). These results provide evidence of nonadditive associations between preweaning forage systems, sire breed of calves, age of dam, and sex of calf in preweaning traits. Consideration should be given to appropriate combinations of these effects in development of efficient cow-calf production systems.