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.

Aggression control in a bachelor herd of fringe‐eared oryx (Oryx gazella callotis), with melengestrol acetate: Behavioral and endocrine observations

“…Our results demonstrate that male fringe-eared oryx fed MGA had reduced fecal androgens associated with a concomitant decline in all forms of agonistic behavior, including both ritualized and escalated aggression. Although other studies have suggested such an effect of MGA on ungulate species [Stover et al, 1987;Blumer et al, 1992;Wilson et al, 2000], this study is the first to quantitatively document the drug's behavioral effects on aggression. In this light it is interesting to note that the effects appear to mediate aggression at all levels, ranging from symbolic posturing to escalated and injurious contact, suggesting specific motivational effects, rather than a general effect on activity level.…”

“…The concentration of MGA the oryx received was determined on the basis of previous studies in which effective contraception was achieved for a variety of species [Raphael et al, 1992;Patton et al, 2000]. A lower dose (0.1 mg/head/day) appeared to decrease aggression in farmed fallow bucks but no decrease in sperm production when compared to controls [Wilson et al, 2000]. As in fallow bucks, when muntjac (Muntiacus reevesi) were treated with MGA (0.02-0.3 mg/day), casual observation of behavior indicated reduced aggression.…”

“…Male muntjacs (Muntiacus reevesi) fed MGA had significantly decreased sperm numbers, and anecdotal reports of behavior indicated reduced aggression [Stover et al, 1987]. Orally administered MGA reduced aggression during the early rut in farmed fallow bucks (Dama dama) [Wilson et al, 2000]. None of these studies, however, systematically quantified aggression before and after MGA administration, leaving the question of efficacy unresolved.…”

Effects of a synthetic gonadotrophin-releasing hormone agonist, leuprolide, on rut-associated events in male red deer

“…Studies with deer have demonstrated some success in suppression of male reproductive activity with synthetic progestagens such as melengestrol acetate (fallow deer Dama dama, Wilson et al 2002) and medroxy progesterone acetate (red deer, Muir et al 1982).…”

Effect of progestins on serum hormones, semen production, and agonistic behavior in the gerenuk (Litocranius walleri walleri)

“…Melengestrol acetate (MGA) has been used widely in domestic cattle to reduce aggressive behavior that might ultimately impact meat quality [Imwalle et al, 2002]. MGA also has been used in farmed fallow deer [Wilson et al, 2002] and the fringe-eared oryx [Patton et al, 2001] to effect aggression control. The aim of this study was to investigate the effects of MPA and MGA on gerenuk serum testosterone concentrations, semen production and agonistic behavior, and to monitor the health of treated animals.…”