Date of this Version
The objective of this study was to determine the effects of different implanting schemes on serum testosterone and cortisol concentrations, and carcass traits of bulls and steers implanted with trenbolone acetate (TBA) and zeranol (Z). Twenty Polled Hereford bulls were randomly assigned to one of three treatments after birth. Five calves served as nonimplanted control bulls (NIB). Nine bulls were implanted (IB) with 140 mg of TBA and 36 mg of Z at about 1 mo of age and reimplanted with both compounds 10 wk later. When IB calves were about 21 wk of age, the TBA implant was removed and calves were reimplanted with Z every 10 wk until slaughter. Six calves were castrated at 3 wk of age and implanted (IS) with TBA and Z every 10 wk until slaughter. Blood samples from each animal were obtained at 144 intervals beginning at 14 wk of age and serum cortisol (C) and testosterone (T) concentrations were determined. The NIB had higher C levels than IB or IS (P < .05) during the preweaning period. During the finishing period, there were no differences in C concentrations between NIB and IB; however, IS had lower levels (P < .05) than both bull treatments. Serum T concentrations began to increase about 12 wk later (42 vs 30 wk, respectively) in IB compared with NIB. Testicular size was smaller (P < .05) in IB than in NIB. No differences (P > .05) were observed in carcass characteristics. Tastepanel scores were not different among treatments. In conclusion, implanting schemes using TBA and Z lowered serum levels of C and delayed puberty in bulls; however, they did not alter carcass characteristics or eating quality.