First Non-Invasive Monitoring of Fecal Steroids in Greater Caribbean Manatees (Trichechus manatus manatus)

Reproductive endocrinology plays a crucial role in the management of endangered species. Using non-invasive techniques, the complex nature of their reproductive biology can be better understood. This study aimed to determine hormonal concentrations of progesterone (P4) and estradiol (E2) in female Greater Caribbean manatees (Trichechus manatus manatus) under human care and to establish whether there are differences in hormone concentrations between sexually mature and sexually immature females based on fecal analysis. The assessment of steroid metabolites was performed using the enzyme-linked immunosorbent assay (ELISA) technique with a commercial DetectX kit. The results indicated reference values for progesterone (P4) ranging from 109.9 to 334.3 ng/g feces and for estradiol (E2) ranging from 12.2 to 90.9 ng/g feces. These results suggest an inversely proportional relationship between the two hormones, demonstrating a complex interaction in the estrous cycle of manatees. The findings also indicated no evidence that individual hormonal levels are correlated (Spearman correlation test: ρ = 0.122, p = 0.254; and Kendall correlation test: τ = 0.084, p = 0.245), although higher progesterone levels were associated with lower estradiol concentrations and vice versa. Similarly, no significant correlation was observed between the hormone concentrations of sexually mature and sexually immature females (Skillings-Mack test: P₄, p = 0.103, df = 34, 10,000 repetitions; E₂, p = 0.276, df = 34, 10,000 repetitions). Longer monitoring periods, along with vaginal cytology and ultrasound evaluations, are recommended.