Endocrine monitoring of the ovarian cycle in captive female Amazonian manatees (Trichechus inunguis).

The Amazonian manatee (Trichechus inunguis; Mammalia: Sirenia), a threatened aquatic mammal endemic to the Amazon basin, is the only sirenian that lives exclusively in fresh water. Information about the reproductive endocrinology of the Amazonian manatee is scarce; therefore, the aim of this study was to monitor salivary progesterone and estradiol patterns during the ovarian cycle in T. inunguis. Salivary samples were collected daily during a 12-week period of two consecutive years from two captive adult females. The salivary estradiol and progesterone were measured by enzyme immunoassay. The results were analyzed in an iterative process of excluding values that were higher than the mean plus 2 standard deviations until the basal values were determined. The interval between two peaks of salivary estradiol followed by a rise of progesterone was considered as one complete cycle for the calculation of the cycle length. We observed only three complete cycles in all samples analyzed. The cycle length ranged from 42 to 48 days (mean of 44.67 days). We also observed two distinct salivary estradiol peaks during all cycles analyzed, with the first peak occurring before the rise in salivary progesterone and the second occurred followed by a return to basal progesterone levels. This is the first in-depth study of the ovarian cycle in Amazonian manatees. Our results demonstrate that salivary samples can be a useful tool in the endocrine monitoring of this species and suggest that T. inunguis shows a peculiar hormonal pattern during the ovarian cycle, a finding that may have physiological and ecological significance in the reproductive strategy of these animals.