Relationship between testosterone and sperm motility in Asian elephants (Elephas maximus): Potential implications during the sexual state of musth

Abstract

Male elephants regularly undergo a unique sexual period of musth that is characterized by elevated testosterone, analogous to the heightened reproductive seasonality of other mammals but distinct because it is nonseasonal and asynchronous among males. Our knowledge of male reproductive biology in elephants is limited compared to females, restricting our ability to effectively manage breeding and ensure optimal welfare, especially during musth. In this study, we analyzed the relationship between serum testosterone concentrations and sperm motility, a measure of semen quality. Semen (n = 152 samples) was collected from four male Asian elephants aged 8 to 47 years housed at the Denver Zoo between 2018 and 2022. For approximately half of the samples (n = 72), serum was also collected within a week of semen collection. Using paired semen and serum samples, we identified significant positive relationships between testosterone concentration and sperm motility in three elephants; the relationship in a fourth elephant trended towards significance. Three elephants exhibited musth during the study; in one elephant, sperm motility was significantly higher during musth, while in the other two, although samples were too limited for statistical analysis, patterns trended the same. Furthermore, two males exhibited increasing motility approaching the start of musth or as musth progressed. Together, these results provide the first evidence of a relationship between testosterone (and perhaps by extension, musth status) and a measure of semen quality in elephants. While further systematic research is warranted, this study has implications for understanding male reproductive activity in a non-seasonally breeding species and motivates innovation in semen collection techniques among Asian elephants to obtain high quality samples even during musth.