Pregnancy- and age-associated variation in serum dehydroepiandrosterone concentrations in black and white rhinoceroses

Abstract Dehydroepiandrosterone (DHEA) is an important hormone precursor for androgen and oestrogen sex steroids, yet it is understudied in wildlife and has not been measured in rhinoceroses. The objective of this study was to examine serum DHEA concentrations in ex situ black (Diceros bicornis; n = 22 male, 18 female) and white (Ceratotherium simum; n = 25 male, 46 female) rhinoceroses. A commercially available DHEA immunoassay was validated for use with rhino serum, and monthly samples (n = 1029) were analysed. Analytical validation included demonstrating parallel displacement curves between serially diluted standards and pooled extracts, as well as 91% extraction efficiency in a spike and recovery test. Differences in DHEA concentrations relative to species, age, sex and pregnancy status were analysed using linear mixed models. Serum DHEA concentrations were higher (P < 0.001) in black (194 ± 14.2 pg/ml) versus white (123 ± 8.0 pg/ml) rhinoceroses and demonstrated a non-linear relationship with age in both species, with concentrations peaking around 15 years of age before declining thereafter. No sex differences between males and non-pregnant females were detected in either rhinoceros species. White rhinoceros DHEA concentrations were higher (P < 0.001) in pregnant (309 ± 31.9 pg/ml, n = 15) compared to non-pregnant (120 ± 10.4 pg/ml, n = 41) females; pregnant black rhinoceroses similarly produced elevated DHEA concentrations during pregnancy (1092 ± 90.3 pg/ml; n = 2) compared to non-pregnant (229 ± 8.1 pg/ml; n = 17) females. DHEA concentrations also increased throughout gestation particularly during mid- to late gestation in both species. These findings provide new insight into rhinoceros endocrinology and suggest potential utility of DHEA for monitoring pregnancy status.