A comparison of fecal steroid metabolite concentrations between harem and bachelor stallions in a free‐Ranging population of przewalski's horses (Equus ferus przewalskii)

Abstract

The aim of this study was to determine whether concentrations of reproductive steroid hormone metabolites significantly differed between harem stallions and bachelor stallions in the free ranging group of Przewalski's horses (Equus ferus przewalskii) at the Hortobágy National Park in Hungary. Throughout the study, fecal samples were collected from 21 harem stallions and 15 bachelor stallions and analyzed for immunoreactive estrogen and androgen metabolites. Harem stallions demonstrated significantly higher concentrations of estrogen (P < 0.001) and epi-androsterone (P < 0.001), but not testosterone (P = 0.426). These findings confirm that sociosexual status has a significant effect on androgen concentrations in individual Przewalski stallions. Zoo Biol. 36:127-131, 2017. © 2017 Wiley Periodicals, Inc.

The Social and Reproductive Challenges Faced by Free-Roaming Horse (Equus caballus) Stallions

“…It has been established that testosterone levels are regulated by the reproductive status of the male; a higher level was observed in harem stallions compared with bachelor stallions [ 36 , 77 ]. This result was not confirmed by [ 78 ], but this study did find higher faecal metabolite concentrations of oestradiol and epi-androstenediol, which are metabolites of testosterone, in harem stallions when compared with bachelors. No differences in ACTH levels and hair cortisol, hormones commonly related to acute and chronic stress responses, were reported between harem and bachelor stallions [ 79 , 80 ], suggesting that bachelor status is not correlated with a higher stress load in stallions.…”

“…It seems that the dominance status of the male and certain individual characteristics can also predict harem tenure. Although the weight of a stallion can predict reproductive success [ 99 ], neither the male’s size, which would be advantageous when fighting [ 100 ], nor his testosterone levels [ 78 ] were found to predict reproductive success. Although it has not been experimentally confirmed, some researchers have proposed that stallions’ individual characteristics in terms of their personality are crucial for successful harem tenure [ 38 , 86 , 101 ].…”

Fecal Glucocorticoid Metabolites as Biomarkers in Equids: Assay Choice Matters

“…In this population, the breeding groups form dispersed subgroups outside the breeding season, which can help mitigate the costs of competition (Stanley et al 2018). As groups become larger, males expend more energy to defend and prevent harassment of females by neighboring males (D'Souza-Anjo et al 2017). Females are less directly affected by group density, the number of sub-groups, and range size (Linklater et al 1999); however, they have elevated glucocorticoids in response to social disruption, instability, and group turnover (Nuñez et al 2014).…”