Effects of GnRH vaccination in wild and captive African Elephant bulls (Loxodonta africana) on reproductive organs and semen quality

摘要

OBJECTIVES:Although the African elephant (Loxodonta africana) is classified as endangered by the InternationalUnion for Conservation of Nature (IUCN), in some isolated habitats in southern Africa,contraception is of major interest due to local overpopulation. GnRH vaccination has beenpromoted as a non-invasive contraceptive measure for population management of overabundantwildlife. We tested the efficacy of this treatment for fertility control in elephant bulls.METHODS:In total, 17 male African elephants that were treated with a GnRH vaccine were examined intwo groups. In the prospective study group 1 (n = 11 bulls, ages: 8±36 years), semen quality,the testes, seminal vesicles, ampullae and prostate, which were all measured by means oftransrectal ultrasound, and faecal androgen metabolite concentrations were monitored overa three-year period. Each bull in the prospective study received 5 ml of Improvac® (1000 μgGnRH conjugate) intramuscularly after the first examination, followed by a booster sixweeks later and thereafter every 5±7 months. In a retrospective study group (group 2, n = 6,ages: 19±33 years), one examination was performed on bulls which had been treated withGnRH vaccine for 5±11 years.RESULTS:In all bulls of group 1, testicular and accessory sex gland sizes decreased significantly afterthe third vaccination. In six males examined prior to vaccination and again after more thanfive vaccinations, the testis size was reduced by 57.5%. Mean testicular height and lengthdecreased from 13.3 ± 2.6 cm x 15.2 ± 2.8 cm at the beginning to 7.6 ± 2.1 cm x 10.2 ± 1.8cm at the end of the study. Post pubertal bulls (>9 years, n = 6) examined prior to vaccinationproduced ejaculates with viable spermatozoa (volume: 8±175 ml, sperm concentration:410-4000x106/ml, total motility: 0±90%), while after 5±8 injections, only 50% of these bullsproduced ejaculates with a small number of immotile spermatozoa. The ejaculates of group2 bulls (vaccinated >8 times) were devoid of spermatozoa. Faecal androgen metabolite concentrationsmeasured in captive males decreased significantly after the fourth vaccination.None of the males entered musth during the treatment period.CONCLUSIONS: Our results showed a marked decrease in semen quality, testicle and secondary sex glandsizes following repeated GnRH vaccinations. After 2±4 years of continuous treatment every5±7 months, the effects were similar to surgical castration.