Effect of Pre- and Postweaning Zeranol Implant on Steer Calf Performance

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Abstract
One hundred ninety-five steer calves were assigned to five zeranol implant treatments (trial 1). Treatments were no implants (0000), two implants during the finishing period (00XX), three implants during growing and finishing periods (0XXX), one implant at 1 to 2 mo of age during the suckling period and two during the finishing period (X0XX) or four implants (XXXX). The growing-period implant was administered at weaning. Weaning weights (211 vs 208 kg) of implanted and nonimplanted suckling calves were not different (P>.05). Calves implanted at weaning, before shipment to the feedlot, had greater (P<.05) weight loss in shipment than nonimplanted calves. In the feedlot, finishing-period daily gains of steers implanted in the growing and finishing period (0XXX) were greater (P<.05) than gains of steers that had received a suckling period implant (X0XX and XXXX). Nonimplanted steer gains were less (P<.05) than gains of steers from the other four treatment groups. Postweaning daily gains and final weights were 1.18 and 517 (0000), 1.26 and 533 (00XX), 1.32 and 551 (0XXX), 1.26 and 540 (X0XX) and 1.25 and 533 kg (XXXX), respectively. Gains and final weights of nonimplanted steers were less (P<.05) than gains of steers implanted only in the feedlot growing and finishing periods (0XXX). In a second trial, 82 steers were assigned either to a 0XXX or XXXX implant scheme. Weaning weights were 11 kg greater (P<.05) for the implanted steers. However, finishing period (1.20 vs 1.12 kg) and postweaning (1.01 vs .96 kg) daily gains (P-<05) and finishing period (6.00 vs 6.70 kg DM/kg gain) feed efficiencies (P<.10) were better for the steer group not implanted in the suckling period (0XXX). Final weights were similar (494 vs 492 kg). These data suggest that implants administered to suckling calves at 1 to 2 mo of age may depress the subsequent response of implants administered at regular intervals from weaning to slaughter. However, overall benefits from implanting and reimplanting throughout the various phases of production are clearly evident Copyright © 1985. American Society of Animal Science. . Copyright 1985 by American Society of Animal Science

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