Ovarian function in the Nile hippopotamus and the effects of Depo-Provera administration

The preliminary results of an investigation into the reproductive endocrinology of the hippopotamus (Hippopotamus amphibius) and the effects of the progestin Depo-Provera on ovarian function are presented. Faecal progestagen analysis indicated that hippos have an oestrous cycle of 29.2 +/- 0.9 days and faecal progestagen concentrations of 323.6 +/- 31.4 ng g(-1) during the luteal phase. Concentrations were higher (765.9 +/- 162.4 ng g(-1); P < 0.05) during pregnancy than during the luteal phase and remained high until parturition. A lactational anoestrus was usually, but not always, observed during nursing. The onset of puberty was observed in three animals and started at 2.5-3.5 years of age. After Depo-Provera treatment, increases in faecal progestagens indicative of ovulation were observed and were not significantly different from luteal concentrations observed before treatment (236.3 +/- 24.4 versus 340.1 +/- 47.9 ng g(-1), respectively); however, the duration of the luteal phase was shorter (P < 0.05) than before treatment (11.3 +/- 1.0 versus 18.9 +/- 1.0 days, respectively). Females returned to normal cyclicity at day 100.7 +/- 15.3 (range 70-116 days) after administration and one female conceived on day 100 after administration.