Effects of Late Castration, Zeranol and Breed Group on Growth, Feed Efficiency and Carcass Characteristics of Late Maturing Bovine Males1

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Abstract
A total of 280 young bulls representing five breed groups with an average age of about 1 yr were assigned to five experimental treatments as follows: (1) emasculator castration at d 0, (2) surgical castration at d 0, (3) intact, (4) intact and implanted at d 0 and 70 with 36 mg of zeranol and (5) intact and implanted at d 0 with 72 mg zeranol. All animals were slaughtered and carcass data were collected after a feeding period of 141 d. Method of castration did not affect rate of gain. Intact males not implanted with zeranol gained 38.6% more (P<.01) during the 141 d period than castrate males. Intact males from the two zeranol implant treatment groups did not differ from each other in gain, but averaged 11.1% more (P<.01) during the 141 d period than males from the intact treatment group not implanted. Castrate males required 40.4% more (P<.01) metabolizable energy (ME) and dry matter (DM)/kg gain than intact males not implanted, but intact males implanted with zeranol did not require less (P>.05) ME or DM/kg gain than intact males not implanted. Males castrated at about 1 yr showed a progressive decrease in secondary sex characteristics during the 141 d feeding period, while males from the three intact treatments showed a progressive increase. Zeranol did not have an effect on testicular weight or on aggressive male behavioral characteristics. Castrate males had greater (P<.01) fat thickness at 12th rib, higher (P<.01) marbling score and lower (P<.01) cutability and retail product percentage than the males from the three intact treatments, which did not differ (P>.05) from each other in traits associated with carcass composition. The effect of treatment on lean color score, though significant, was not of major importance; all treatments produced meat of acceptable color. The longissimus muscle of castrate males had a finer texture (P<.01) than longissimus muscle from males from intact treatments, which did not differ from each other (P>.05). Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science.

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