Abstract
Twenty-eight Simmental bull calves were randomly allotted to one of three treatments at birth. Ten bulls (IB) and nine steers (IS), castrated within 3 days of birth, were implanted with oestradiol (E 2). The remaining calves were non-implanted, control bulls (CB). Calves were implanted within 3 days of birth and at 200-day intervals until slaughter at 14·8 months of age and at a mean carcass weight of 381·6 kg. Blood samples were taken every 14 days from 9·8 through 14·8 months and serum was analyzed for E 2 and testosterone (T) levels. Carcasses were chilled in a 3 to 7°C cooler. Carcass data were obtained and aged longissimus dorsi steaks were evaluated by a trained sensory panel and a Warner-Bratzler shear (WBS) device. Scrotal circumferences were smaller ( P < 0·0.5) for IB than for CB. Control bulls had heavier weaning weights ( P < 0·05) than IB and higher ( P < 0·05) feedlot gains than IS. Implanted steers required more ( P < 0·05) feed/unit of gain than CB and IB. Implanting bulls with E 2 increased ( P < 0·05) serum E 2 levels and tended ( P < 0·10) to reduce T levels. Serum E 2 in IS and IB were drastically increased ( P < 0·05) for 4 to 6 weeks following re-implantation during the feedlot phase, then sharply declined. Implanted steer carcasses had more youthful maturity scores than CB carcasses. The incidence of hear ring (dark, coarse, band formation) was greater ( P < 0·05) for IB than for IS, probably because of the thinner fat cover ( P < 0·05) on IB. Ribeye areas were smaller ( P < 0·05) and yield grades were higher for IS than for CB. Testicle weights were not significantly different between IB and CB, although variability was greater for IB. Carcass masculinity was least ( P < 0·05) for IS, and IB were less ( P < 0·05) masculine than CB. The only difference in longissimus dorsi sensory traits was that steaks from IB were juicier than steaks from CB. Also, WBS values were lower ( P < 0·05) for IS than for CB.
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