Effects of the Administration of a Long-Lasting GNRH Analogue in the Male Scimitar-Horned Oryx (Oryx dammah)
The scimitar-horned oryx (Oryx dammah) is listed as extinct in the wild, but the species is well represented in captive institutions around the world. Only selected subjects are recruited into coordinated captive breeding programs. The management of subjects not involved in breeding programs may be problematic, as males display unwanted aggressive behavior and can mate with females leading to undesired pregnancies. Orchiectomy is an irreversible solution, and development of methods allowing the possible recovery of the subjects to reproduction are more desirable. In several species, the administration of subcutaneous implants of Deslorelin can inhibit the hypothalamic-pituitary-gonadal axis (HPG axis) leading to temporary suppression of fertility.
So far, scarce information1 about the use of Deslorelin on the male scimitar-horned oryx is available, therefore this work aimed to document the effects of the Deslorelin administration by monitoring the subjects’ clinical conditions, behavior and fecal androgen concentrations. The use of [sic].
Four intact male oryxes (Mi1-4) were sedated and administered with subcutaneous implants of Deslorelin to temporarily suppress reproduction and inhibit aggressive behaviors. At this time, physical examination, complete biochemistry and hematology did not show any abnormalities. Maximal testicular diameter was also recorded. Implants were administered in summer, and dosages varied (Mi1 and Mi2; 14.1mg, Mi3; 18.8mg, and Mi4; 9.4mg). Three months later, animals Mi2 and Mi3 were excluded from the trial for clinical reasons and eventually died. The following year, Mi1 received a second treatment (9.4 mg). Clinical examinations were repeated 90 days after implant insertion (Mi1, Mi2, Mi3), at the time of the second implant insertion (11 months after the first implant insertion; Mi1 and Mi4) and 18 months after the first implant insertion.
Individual behavior was observed 1–2 days/week (focal animal sampling, 20 min/d) for 2 months before (BI) and 2 months post implant insertion (PI). Fecal samples were collected once or twice a week for 2 months before and 6 months after the implant insertion.
To extract the androgen from the fecal matrix, wet fecal samples (200 mg) were boiled in 90% ethanol; the extracts were dried under nitrogen flow and then dissolved in phosphate buffer saline (PBS). Androgen concentrations were measured by a specific radioimmunoassay, using an antiserum raised against testosterone-3 carboxymethyloxime-BSA, 3H testosterone as the tracer and native testosterone as the standard. The fecal androgen concentrations measured in the treated subjects were compared with those measured in one female (F) and one orchiectomized male (Mo) (n=13 samples collected on different days).
Animals did not show any significant alterations in hematological or biochemical parameters during the experimental period. On day 0, average testicular diameter was 21.7±1.0 (mean±s.e.m). After 90 days, animals Mi2 and Mi3 showed a decrease in maximum testicular diameter (10% and 12%, respectively).
In contrast with the results of previous studies1, during the first treatment a significant increase of activity levels (moving, alert and agonistic behavior; P<0.05) was observed in all the subjects PI, probably in response to the temporary increase of testosterone level induced by Deslorelin. After one month, animals returned to normality and had less exhibition of agonistic and reproductive behaviors, but the dominant male, Mi3, continued displaying courtship behaviors, without mounting. Some temporary changes in the dominance hierarchy occurred PI, in contrast with the results reported by Penfold et al.1 After the death of the dominant subject (Mi3) and of Mi2, Mi1 became dominant and, despite the implant, kept showing reproductive behaviors.
Prior to implant insertions, fecal androgens were significantly higher (P<0.001) in Mi1, Mi2 and Mi3 than in Mo or F (range: Mi1=11.1–42.6 ng/g; Mi2=14.4–44.8 ng/g; Mi3=27.4–70.0 ng/g; Mo=7.8–23.3 ng/g; F=8.2–10.8 ng/g). The androgen response to Deslorelin administration was variable among subjects, and Mi3 showed the highest concentrations throughout the experimental period. A significant increase in mean fecal androgen concentrations (P<0.01) was observed during first week after implant insertion followed by a gradual decrease; however, mean fecal hormone concentrations in Mi were never below those observed in F and Mo (P<0.01). The range of fecal androgens was 9.2–47.9ng/g in Mi1, and 11.8–52.0 ng/g in Mi4 from days 0 to 74 after implant insertion, suggesting incomplete HPG axis inhibition, as suggested by Penfold et al.1 The fecal androgen profiles in treated males did not allow determining the duration of the implants’ effectiveness.
In conclusion, the subcutaneous Deslorelin administration did not completely suppress the HPG axis, and the four males showed different responses in terms of behavior and fecal androgen concentrations. Mi3 showed both a dominant character and displayed the highest fecal androgen level. After the first implant, no animal showed mounting behaviors and none of the females conceived. However, after the second implant, Mi1 displayed all reproductive behaviors, including mounting.
We are grateful to Dr. Davide Guadagnini, director of Faunistic Park―Le Cornelle‖, for his contribution, and to Dr. Laura Da Dalt, for her technical assistance.
1. Penfold LM, Ball R, Burden I, Jöchle W, Citino SB, Monfort SL, Wielebnowski N. 2002. Case studies in antelope aggression control using a GnRH agonist. Zoo Biol, 21:435–448.