Detection of fetal gender differences in maternal serum progesterone concentrations of Asian elephants (Elephas maximus)

Previous studies have analyzed total testosterone concentrations in maternal serum for a reliable method of fetal gender determination in Asian elephants (Elephas maximus). The present study investigated the possibility that progesterone concentrations in maternal serum may reflect these testosterone patterns. Weekly serum samples were collected from 17 pregnancies in captive Asian elephants and analyzed via radioimmunioassy (RIA) for progesterone concentrations. Nine and eight cows carried male and female calves, respectively. Mean progesterone concentrations in maternal serum of elephants carrying male calves were greater than in those carrying female calves (P < 0.01). Mean progesterone concentrations (based on 5-week means) in maternal serum were greater at weeks 20–55 (P < 0.01) and 60–65 (P < 0.05) for elephants carrying male calves.