Progesterone monitoring and gestation length in Amazonian manatees (Trichechus inunguis)

Knowledge of pregnancy length and the physiological parameters during pregnancy is an important tool for pregnancy diagnosis in free-ranging and captive individuals and for the correct husbandry of captive pregnant females. Therefore, this study aimed to describe the progesterone pattern during pregnancy in T. inunguis and to estimate the pregnancy length in this species. Blood or urine samples from a total of eight pregnancies were collected from six captive female Amazonian manatees. Serum progesterone and urinary progesterone metabolites were measured by radioimmunoassay and enzyme immunoassay. The mean of serum progesterone throughout pregnancy was 5.17 ± 4.71 ng/ml (0.08–19.71 ng/ml) and the mean urinary progesterone metabolites concentration was 11.34 ± 12.28 ng/mg Cr (1.00 – 54.71 ng/mg Cr). A pregnancy length of approximately 12–13 months was observed (369.6 ± 27.2 days, range 352–401 days). The pregnancy length observed in this study falls within the range reported for other sirenians. During the first four months, there was a high level of progesterone. After that, the hormone levels began to decrease. Low progesterone levels during most of pregnancy were also observed in other sirenians. This hormonal pattern suggests the existence of the paracrine action of progesterone or the role of other hormones in the maintenance of pregnancy. However, further studies are necessary to clarify the pregnancy endocrinology in Amazonian manatees.