Effect of anabolic hormone exposure during the backgrounding-phase in calf-fed steers of different mature sizes.

The mature size (MS) of cows in the United States is diverse, which leads to diversity in the MS of feeder cattle and hot carcass weights (HCW) of fed cattle. Cattle feeders must manage this inherent variation. Given that implants alter MS, they may be an effective tool to manage variation in HCW across groups of cattle. Two experiments were conducted to evaluate the interaction of MS and implant status in calf-fed steers. Steer calves from the same two sources were used in both experiments. Because breeding seasons were <60 d, it was assumed that weaning weight (WW) to a large extent reflected differences in MS. Smaller MS (SMS) and larger MS (LMS) steers were identified from the tails of the WW distribution. Within each MS group, steers were implanted with 20 mg estradiol benzoate and 200 mg progesterone (SS) or 14 mg estradiol benzoate and 100 mg trenbolone acetate (CH) on d 1 (Exp. 1), and nonimplanted (NI) or implanted with SS on d 2 (Exp. 2). In both experiments, a common terminal implant was used and steers were fed for 161 (Exp. 1) and 168 d (Exp. 2). Data were analyzed as a randomized complete block design with a 2 × 2 factorial treatment structure, with main effects of MS and implant. No MS × implant interactions were observed in either experiment (