Sire Differences for Growth and Carcass Traits of Purebred Brahman Steers.

Purebred Brahman steers (n = 169) sired by 23 Gray and 8 Red Brahman bulls were evaluated for postweaning growth and carcass traits. Spring-born paternal half-sib male calves were purchased from private producers at weaning, backgrounded, and grazed on ryegrass for an average of 161 d. Following grazing, the steers were shipped to a commercial feedlot in south Texas for feeding. Steers were slaughtered in groups of about 45 head when they reached an approximate average endpoint weight of 530 kg and 1 cm backfat. All carcasses were subjected to high voltage electrical stimulation during slaughter. After a 24 hr chill, carcasses were ribbed, data collected, and a longissimus muscle sample taken for calpastatin assay. Traits of interest were feedlot average daily gain, slaughter weight, hot carcass weight, backfat measured at the 12th rib, loin-eye area, loin-eye area per 45.4 kg of carcass weight, marbling score, quality grade, yield grade, calpastatin, shear force at 7 and 14 days of aging, and hump height. Two 2.54 cm thick steaks were removed from the large end of the strip loin, vacuum packaged, and randomly selected for 7 or 14 d. Steaks were then cooked to an internal temperature of 70°C and core samples measuring 1.27 cm were taken for shear force determination. A mixed model containing cow age and steer slaughter age as fixed covariates and sire as a random variable was used to analyze the data. BLUP estimates of sire expected progeny differences were obtained for all traits. Sire was a significant source of variation for all traits except for marbling and quality grade. Gray Brahman steers had heavier slaughter weights, heavier hot carcass weights, greater backfat, more marbling, less calpastatin, and were more tender at 14 d of aging when compared to Red Brahman steers (P < .05). Red Brahman steers had more desirable yield grades with larger loin-eye area per 45.4 kg of carcass weight (P < .05). These results indicate significant variation within the Brahman breed and useful genetic differences among Brahman sires for several growth and carcass traits.