title: Effect of zeranol or melengestrol acetate (MGA) on testicular and antler development and aggression in farmed fallow bucks.
abstract: Fifteen yearling fallow bucks were randomly assigned by BW to one of three treatment groups: control (C; n = 5), melengestrol acetate (MGA; n = 5), and zeranol (Z; n = 5), to evaluate effects on testicular development, aggressive behavior, antler growth, sexual activity, ADG, and BW. Zeranol-treated bucks received zeranol ear implants (36 mg) at 90-d intervals, and MGA-treated bucks received MGA in the ration (100 microg x animal(-1) x d(-1)). Bucks grazed ryegrass/Coastal bermudagrass pasture and were supplemented with 3:1 corn/soybean meal at 0.45 kg x animal(-1) x d(-1). Body weights, body condition scores (BCS), blood samples, and testis measurements were obtained at d 0 and at 14-d intervals for 229 d. As bucks reached hard antler (7/15 to 8/25), antlers were harvested and weighed, and ejaculates were collected at 14-d intervals. Aggression was evaluated using 10-min video sessions scoring body blows, avoidance, head pushes, and head bunts. Scrotal circumference (SC) and paired testis volume were affected by a day x treatment interaction (P < 0.01); testes of zeranol-treated bucks were smaller than those of control or MGA-treated bucks. First sperm in the ejaculate tended to be delayed (P < 0.10) in zeranol-treated bucks compared with control and MGA-treated bucks. Melengestrol acetate-treated bucks had a maximum sperm concentration in the ejaculate that was three times (P < 0.05) that of control bucks and nine times (P < 0.05) that of zeranol-treated bucks. Antler weight was the least (P < 0.01) for bucks receiving zeranol and greatest (P < 0.10) for MGA-treated bucks; intermediate values were recorded for the control bucks. Aggressive behavior was delayed (P < 0.05) for zeranol-treated bucks until treatment effects were overcome. Melengestrol acetate-treated bucks had decreased (P < 0.01) aggressive behavior compared with control bucks. Melengestrol acetate-treated bucks had increased (P < 0.05) serum testosterone concentrations compared with control and zeranol-treated bucks. Human chorionic gonadotropin-stimulated peak serum testosterone concentrations for zeranol-treated bucks were delayed (P < 0.01) compared with control and MGA-treated bucks. Although zeranol-treated bucks overcame treatment effects, they were never able to reach testicular measurements or sperm concentrations equal to those of the control or MGA-treated bucks. Zeranol and MGA treatments may have both positive and negative effects that can be utilized when producing slaughter bucks.
authors.affiliation: Texas A&M University Agricultural Research and Extension Center, Overton 75684, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Wilson
authors.forename: D A
authors.initials: DA
authors.lastname: Neuendorff
authors.forename: A W
authors.initials: AW
authors.lastname: Lewis
authors.forename: R D
authors.initials: RD
authors.lastname: Randel
mesh_terms: D000374:Aggression / Q000187:drug effects; D000818:Animals; D000999:Antlers / Q000187:drug effects / Q000254:growth & development; D001522:Behavior, Animal / Q000187:drug effects*; D003670:Deer / Q000254:growth & development / Q000502:physiology* / Q000523:psychology; D004343:Drug Implants; D004968:Estrogens, Non-Steroidal / Q000494:pharmacology*; D008297:Male; D008552:Melengestrol Acetate / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D045167:Progesterone Congeners / Q000494:pharmacology*; D011897:Random Allocation; D012611:Scrotum / Q000033:anatomy & histology / Q000187:drug effects; D012741:Sexual Maturation / Q000187:drug effects; D013076:Sperm Count / Q000662:veterinary; D013737:Testis / Q000187:drug effects / Q000254:growth & development; D013739:Testosterone / Q000097:blood; D015430:Weight Gain / Q000187:drug effects; D015029:Zeranol / Q000494:pharmacology*
chemical_list: D004343:Drug Implants; D004968:Estrogens, Non-Steroidal; D045167:Progesterone Congeners; D013739:Testosterone; D008552:Melengestrol Acetate; D015029:Zeranol