Urinary steroid evaluations to monitor ovarian function in exotic ungulates: V. Estrogen and pregnanediol‐3‐glucuronide excretion in the black rhinoceros ( Diceros bicornis )

A study of female black rhinoceros ( Diceros bicomis ) urinary steroid and steroid metabolite excretion was performed to determine if techniques useful for monitoring reproductive events in the Indian rhinoceros ( Rhinoceros unicornis ) could be utilized to evaluate the black rhinoceros. Urine samples from 19 zoo‐held black rhinoceros were analyzed for estrogen, estrone conjugates (EC), and pregnanediol‐3‐glucuronide (PDG) content by direct radioimmunoassays. Estrogen analysis revealed that >95% of the estrogens present in female black rhinoceros urine are conjugated, with estrone and estradiol accounting for virtually all of these estrogens. There is no observable difference in the amount of estrogen present in estrus; postestrus; and early‐, mid‐, and late‐gestation urine samples. Analysis of serial urine samples for EC failed to reveal any discernible levels or patterns which reflected reproductive status. Neither nonpregnant nor early‐gestational female black rhinoceros' urine samples contained detectable amounts of PDG. Urinary PDG concentrations became measurable in midgestation (9–12 months prior to parturition) and rose steadily throughout the remainder of gestation. PDG levels declined sharply and became nondetectable 1 day postpartum. Though a wide range in PDG levels was observed among individual pregnant animals, each female consistently excreted increasing amounts of PDG through latter pregnancy.