Effect of immunocastration with a gonadotropin-releasing hormone vaccine in a male zebra Equus quagga boehmi

Abstract

Grant’s zebra Equus quagga boehmi is an equine species commonly bred in zoos under human care. Male zebras are often castrated to prevent a surplus captive zebra population. Gonadotropin-releasing hormone (GnRH) vaccination may pose an alternative to surgical castration. The aim of this study was to evaluate the effects of an anti-GnRH vaccine on testosterone concentrations in a male zebra. A harem of one male and three adult female Grant’s zebras were included in the study. The male was immunised with 4 ml (600 µg GnRH protein conjugate) of a commercially available anti-GnRH vaccine (Improvac®) administered on five occasions at an interval of 4 weeks for the first and second dose and 12-week and 6-week intervals for the remaining doses. Faecal metabolites of testosterone were determined weekly for 1 year. In addition, faecal progesterone and estradiol metabolites were measured in one female after parturition. The GnRH vaccine failed to reduce testosterone metabolite concentrations, and in one female, pregnancy was confirmed through faecal progesterone and estradiol metabolite concentrations. Furthermore, fertility of the male was verified by detection of pregnancy in all three females. Therefore, the GnRH vaccine protocol used here was not effective as immunocastration in the treated male zebra. Further investigations should consider a larger number of animals, a higher dose, and four to five injections with an administration interval of 4 weeks.