Effects of growth promoting implant strategies on performance of pre- and postweaned beef calves

One hundred crossbred steers (BW = 166 ± 26.6 kg) were stratified by birthdate over 2 yr and assigned to 1 of 3 treatments: NI: not implanted; WN: implanted only at weaning with 40 mg of trenbolone acetate + 8 mg of estradiol; and CF: implanted twice-once with 100 mg of progesterone + 10 mg of estradiol at calfhood vaccination (100 d of age) and once at weaning with 40 mg of trenbolone acetate + 8 mg of estradiol. Calf BW was recorded at weaning and on d 28, 45, and 80. At d 80, intramuscular fat, fat thickness over the 12th rib, LM area, and rump fat were measured via ultrasound. Because of dry conditions, calves in yr 1 were early weaned, whereas calves in yr 2 were weaned normally. Data were analyzed separately for 2 yr using a linear model. In yr 1, CF had greater prewean BW gain (P = 0.04) compared with their counterparts, and WN and CF had greater ADG 28 d after weaning and a tendency (P < 0.14) for greater ADG after weaning. In yr 2, CF and WN had greater BW, ADG, and total BW gain for the overall postweaning period (P ≤ 0.05). Both CF and WN had greater lifetime ADG compared with NI in both years (P ≤ 0.04). All 3 treatments differed (P = 0.05) among each other in yr 2, with CF and WN having the least amount of intramuscular fat. Results suggest that variable results to growth promoting implants are noted when applied at different stages of calf production.