Assisted reproduction is still underutilized in rhinoceros breeding programs considering that many individuals cope with sub or infertility, silent oestrus, anoestrus, early embryonic death or stillbirth.2 Specifically, in greater one-horned (GOH) rhinoceros (Rhinoceros bicornis), irregular cycles or anoestrus with subsequent formation of haemorrhagic follicles represent a challenging problem.1 While hormone activity can be closely monitored in GOH rhinoceros means to induce ovulation and thus enhance breeding efforts in anoestrous females have never been published. In this study hcG and GnRH were tested for their ability to induce ovulation in GOH rhinoceros. Follicular development was closely monitored in one female by transrectal ultrasound. Development of a pre-ovulatory follicle as a prerequisite of ovulation induction took 26.9±4.4 days (n=9). Particularly, fast follicular growth of 0.5 cm/d was observed during the last 7 days of dominant follicle development. When a pre-ovulatory follicle was present (11.9±0.2 cm), ovulation was induced by i.m. injection of either hcG or GnRH. Successful induced ovulation was determined by presence or absence of the ovulatory follicle 1–3 days after the treatment and by the increase of 20-oxo-gestagene concentration in the feces. Ovulation in the anestrous female GOH rhinoceros was successfully induced in 78% (7/9) of the treatments regardless of the hormone used, hcG or GnRH. hcG induced 4 (4/6) while GnRH induced 3 (3/3) ovulations. We, therefore, conclude that both hcG and GnRH have the potency to induce ovulation in GOH rhinoceros.
1. Stoops MA, Pairan RD, Roth TL. Follicular, endocrine and behavioural dynamics of the Indian rhinoceros (Rhinoceros unicornis) oestrous cycle. Reproduction. 2004;128:843–856.
2. Stoops MA, Campell MK, DeChant CJ, Hauser J, Kottwitz J, Pairan RD, Shaffstall W, Volle K, Roth TL. Enhancing captive Indian rhinoceros genetics via artificial insemination of cryopreserved sperm. Anim Reprod Sci. 2016;172:60–75.