Measurement of urinary oestrogens and 20 alpha-dihydroprogesterone during ovarian cycles of black (Diceros bicornis) and white (Ceratotherium simum) rhinoceroses.

The development of a sensitive enzyme-immunoassay for 20 alpha-dihydroprogesterone (20 alpha-DHP) and its use in determining reproductive status in black and white rhinoceroses is reported. 20 alpha-DHP in hydrolysed urine diluted in parallel to standards, and high-performance liquid chromatography (HPLC) confirmed the presence of 20 alpha-DHP and the absence of pregnanediol-3 alpha-glucuronide (PdG) in urine collected from rhinoceroses after oestrus. Conjugated oestrone was identified by HPLC as the major urinary oestrogen in the black rhineroceros and conjugated oestradiol-17 beta was the most abundant in the white rhinoceros. In African species, the black (Diceros bicornis), and northern (Ceratotherium simum cottoni) and southern (Ceratotherium simum simum) white rhinoceroses, excretion of 20 alpha-DHP and oestrogen followed a cyclic pattern. Excretion of 20 alpha-DHP was low before mating, at the time of peak oestrogen excretion, but high after oestrus. In the black rhinoceros, the follicular phase was 3-4 days and the luteal phase was 18 days, suggesting a cycle of 21-22 days. The interoestrus interval in the northern subspecies of white rhinoceros was 25 days, which correlated well with the interval between peaks of oestradiol-17 beta excretion. The interval between urinary oestrogen peaks in the southern subspecies of white rhinoceros suggested a cycle length of 32 days. This paper provides the first description of the pattern of excretion of urinary oestrogens and progesterone metabolites in African rhinoceroses.