[en] Animals ; Body Composition/drug effects ; Body Weight/drug effects ; Cattle/growth & development ; Creatinine/blood ; Drug Implants ; Estradiol/administration & dosage/pharmacology ; Estrenes/pharmacology ; Growth Hormone/blood ; Male ; Trenbolone/administration & dosage/pharmacology ; Urea/blood
[en] Twelve (Exp. 1) and 24 (Exp. 2) young growing bulls were used to compare the effects of long-acting, cholesterol-based implants with short-acting, lactose-based implants. Each implant contained 200 mg of trenbolone acetate and 40 mg of 17 beta-estradiol. The long-acting, cholesterol-based implants were applied once either 18 wk (early implantation) or 12 wk (late implantation) before slaughter. The lactose-based pellets were implanted once (6 wk before slaughter), twice (12 and 6 wk) or three times (18, 12 and 6 wk) before slaughter. Treated animals had higher live weight gains, a lower feed conversion ratio, a higher proportion of lean meat and a lower proportion of adipose tissue than control animals. In Exp. 1 live weight gain of bulls implanted early with a single cholesterol-based implant was similar to the gain of animals treated three times with a lactose-based implant, but in Exp. 2 the effects of the long-acting implants given early were not sustained. In Exp. 3, 24 young growing bulls were used in a 3 X 2 factorial design to compare the effects of three dose levels of trenbolone acetate (100, 200 and 300 mg) and two levels of 17 beta-estradiol (40 and 60 mg). There were no significant differences between treatment groups, but highest live weight gains were observed in animals implanted with 300 mg of trenbolone and 60 mg of estradiol. This group also yielded the highest proportion of lean meat and the lowest proportion of adipose tissue. There was a decrease in plasma urea concentration after each implantation. It appeared also that plasma trenbolone was higher with implants containing 60 mg of estradiol. There were no differences between groups in growth hormone response to arginine stimulation.