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

Abstract

The development of a sensitive enzyme-immunoassay for 20α-dihydroprogesterone (20α-DHP) and its use in determining reproductive status in black and white rhinoceroses is reported. 20α-DHP in hydrolysed urine diluted in parallel to standards, and high-performance liquid chromatography (HPLC) confirmed the presence of 20α-DHP and the absence of pregnanediol-3α-glucuronide (PdG) in urine collected from rhinoceroses after oestrus. Conjugated oestrone was identified by HPLC as the major urinary oestrogen in the black rhinoceros and conjugated oestradiol-17β 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 20α-DHP and oestrogen followed a cyclic pattern. Excretion of 20α-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 inter-oestrus interval in the northern subspecies of white rhinoceros was 25 days, which correlated well with the interval between peaks of oestradiol-17β 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.