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Effects of Late Castration, Zeranol and Breed Group on Growth, Feed Efficiency and Carcass Characteristics of Late Maturing Bovine Males^1,2,

US Department of Agriculture³, Clay Center, NE 68933

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).

¹ The authors gratefully acknowledge the assistance of R. Sampson, J. Green and M. Barkoff in collecting growth and feed consumption data, of M. Self for collecting carcass data and of W. Hinerman and R. Bauer for analysis of the data.

² Zeranol implants were provided by International Mineral and Chemical Corp., Terre Haute, IN 47808.

³ Roman L. Hruska U.S. Meat Animal Research Center, ARS.