Determination of serum anti-Müllerian hormone, estrogen and progesterone concentrations in prepubertal red foxes (Vulpes vulpes L.).

This study aimed to characterize the endocrine profiles and associated vaginal cytological shifts in prepubertal red foxes (Vulpes vulpes). Eighteen foxes (3-11 months) were evaluated following clinical recovery at a regional rehabilitation center. Subjects were stratified by age (Y1: 3-5 months, n = 11; Y2: 6-11 months, n = 7) and body weight (A1: 2-3.5 kg, n = 10; A2: 3.6-6 kg, n = 8). Morphometric measurements of the vulva, exfoliative vaginal cytology, and serum concentrations of estrogen (E2), progesterone (P4), and anti-Müllerian hormone (AMH) were analyzed. To prioritize animal welfare and minimize capture stress, sampling was conducted in a single instance upon clinical readiness. Vulvar dimensions and E2 levels increased significantly with age (P < 0.05), whereas fluctuations in AMH and P4 remained statistically non-significant (P > 0.05). Endocrine variations based on body weight did not reach statistical significance. However, vaginal cytology revealed a significant age-dependent decrease in basal-parabasal cell density alongside an increase in small intermediate cells (P < 0.05). These findings suggest that prepubertal red foxes undergo discernible reproductive maturation as they approach puberty, characterized by synchronized shifts in estrogenic activity, vulvar morphometry, and vaginal epithelial cornification. This study provides the first preliminary endocrine data for AMH in this species, mirroring physiological patterns established in domestic canids.