Reproductive endocrinology of endangered black-footed ferrets: implications for conservation breeding

The black-footed ferret (Mustela nigripes) is an endangered North American mustelid. This species is bred in managed care with the goal of reestablishing wild populations. However, individual ferrets in the conservation breeding programme have variable reproductive success. We monitored faecal steroid hormone metabolite profiles of 22 black-footed ferrets across two breeding seasons to examine whether endocrine factors were associated with successful reproduction. Among successfully whelping females, faecal progesterone metabolite concentrations were higher (P = 0.04) and faecal cortisol metabolite (FCM) concentrations were marginally higher (P = 0.07) in the late luteal phase compared to females who did not whelp (likely pseudopregnant). Effect sizes suggested that, in successfully whelping females, faecal oestradiol metabolite levels were higher in the follicular phase and FCM levels lower in the early luteal phase, but with high variation and lack of statistical significance. We speculate that this variation may be because male causes of reproductive failure account for some of these cases of pseudopregnancy. Among males, individuals that failed to successfully copulate had lower faecal testosterone metabolite concentrations than successful sires (P = 0.01). However, males who copulated but failed to sire a litter did not differ from successful sires in testosterone metabolite concentrations. Comparisons of sperm morphology between successful and unsuccessful sires were statistically underpowered, hence poor sperm quality could not be ruled out as a possible cause of these post-copulatory reproductive failures. Our data suggest that individuals who fail to reproduce in managed care are not experiencing chronic stress, based on FCM levels, although changes in females during the early luteal phase warrant further investigation. While male post-copulatory reproductive failure was not associated with deficiencies in sex hormone production, males that fail to copulate could potentially be targeted for testosterone supplementation.