The Influence of Zeranol Implants in Bulls, Late Castrates and Steers Fed for Slaughter

133 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.Intact bovine males gain more rapidly and efficiently than castrates, however, feedlot behavior and tenderness problems have been encountered. Two trials were conducted to determine the effects of zeranol implants in intact males (bulls) and castrates (steers). The effects of late castration were also studied. A factorial arrangement of treatments was utilized to determine effects of castration, postweaning zeranol implantation and breed (Angus vs Limousin) on growth, behavior and carcass traits. Bulls outgained steers and did not require more days-on-feed to a fat endpoint of .76 cm. The implant did not influence gain in bulls but did increase gain in steers. Angus and Limousins were similar in growth rate but Limousins required more days-on-feed. Bulls and Limousins produced heavier carcasses and larger ribeyes. Steers and Angus had higher marbling scores. Implanting decreased marbling and increased carcass maturity. Bulls were quieter during weighing and mounted more frequently in the pen than steers. Limousins mounted more frequently than Angus. Warner-Bratzler shear (WBS) determinations and taste panel evaluations were performed on five major muscles. Angus cattle had lower WBS values than Limousin for three of the muscles studied. Steers had numerical advantages over bulls in many taste panel traits, however few significant differences were noted. The implant tended to have negative effects on palatability. Bulls had less intramuscular lipid and more collagen in the longissimus muscle. Results suggest that selection of early maturing breeds may be critical to insuring acceptable palatability of young bull beef. In a second trial the effects of 0, 36 and 72 mg zeranol implants were evaluated in intact and late castrated males. A 36 mg implanted steer treatment, castrated at the beginning of the trial, was the control. Implanted intact males grew more rapidly than non-implanted males, but there was no advantage to the higher initial dosage level. Bulls outgained late castrates. There was no significant difference in taste panel evaluations. Results indicate that delaying castration does not appear to provide economic advantages.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD