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Effects of Zeranol Implantation and Late Castration on Sexual, Agonistic and Handling Behavior in Male Feedlot Cattle^1,2,

University of Illinois, Urbana 61801

Abstract

Seventy-two Angus feedlot bulls were observed to determine the effects of implanting with zeranol (0, 36 or 72 mg; four groups of six/level) at 8 mo of age (d 0), and of castration midway through the feedlot period (d 115) vs remaining intact (six groups/treatment) on sexual, agonistic and handling behaviors. All 36-mg-treated cattle were re-implanted (36 mg) on d 112; 72-mg-treated cattle were not re-implanted. Each group was observed for a total of 8 h at the time of sunset ± 30 min for sexual and agonistic behaviors during the trial. Observations on handling were made during 15 weighings and on seven occasions in the pens of the animals. Zeranol did not affect sexual or agonistic behavior. Before imposition of castration, implanted bulls entered the scales more quickly, took longer to stand still on the scales and were less quiet than non-implanted bulls (P<.05). Castration decreased the sexual behaviors of masturbation (.75 vs .08 · pen^–1 · h^–1; P<.05), attempted mounts (.75 vs .33 · pen^–1 · h^–1; P<.05) and chinning (10.70 vs 4.75 · pen^–1 · pen^–1; P<.10) and the agonistic behavior of butting (42.42 vs 31.50 · pen^–1 · h^–1; P<.01) in contrast to intact bulls. Castrated animals entered (P<.10) and exited (P<.05) the scales more quickly than did intact males. Zeranol implants were associated with decreased butting in intact males and increased butting in castrated males (P<.01). Serum testosterone levels were higher in implanted compared with non-implanted bulls on d 107 post-implantation (P<.01), but re-implanting tended to decrease testosterone levels (P<.10).

¹ This study was made possible in part by a grant from Int. Minerals and Chemical Corp., Terre Haute, IN.

² The authors express appreciation to the crew of the beef farm, D. J. Kesler, Cindy Petrie and Kristie Rohde for their assistance during the study and to R. Fernando and G. R. Frank for statistical guidance.

³ Dept. of Anim. Sci.

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