Effects of late castration, zeranol and breed group on growth, feed efficiency and carcass characteristics of late maturing bovine males.

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 less than .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 less than .01) during the 141 d period than males from the intact treatment group not implanted. Castrate males required 40.4% more (P less than .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 greater than .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 less than .01) fat thickness at 12th rib, higher (P less than .01) marbling score and lower (P less than .01) cutability and retail product percentage than the males from the three intact treatments, which did not differ (P greater than .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 less than .01) than longissimus muscle from males from intact treatments, which did not differ from each other (P greater than .05).