Reproductive Cycle of the Asian Elephant (Elephas Maximus) in Captivity 1

Serum samples were obtained either weekly or daily from six mature elephant cows for periods of 7 to 30 months from April 1979 to November 1981, to rigorously describe the hormonal and behavioral components of the reproductive cycle in the Asian elephant. The estrous state of each elephant was concurrently monitored through quantification of the frequency of male urine testing behavior (Flehmen-like response) under controlled conditions. Concentrations of progesterone (P4) and estradiol (E2) were determined in 1.0 ml of serum by radioimmunoassay (RIA) after diethylether extraction and purification on Sephadex LH-20 columns. The presence of gonadotropic activity was assessed with a rat luteinizing hormone (LH) RIA and by an in vitro mouse Leydig cell bioassay. Fifteen ovarian cycles averaging 16.3 ± 0.4 (mean ± SEM) weeks in length were observed in six females. The luteal phase was 10.5 ± 0.3 weeks, and 5.1 ± 0.4 weeks separated subsequent luteal periods. Estradiol concentrations were extremely variable, and no distinct preovulatory E2 surge was associated with the onset of P4 secretion. However, the onset of P4 release occurred during a single 24-h period and reached maximum levels within 2 to 3 weeks. Peaks of immunoreactive LH were observed, although more than 50% of such “surges” were unrelated to increments in P4 secretion, and no evidence of bioactivity was observed in any serum sample. Pregnancy was indicated by continued secretion of P4 after the 12-week luteal phase, and elevated levels (400 to 1200 pg/ml) were seen throughout the first year and during the last 6 months of gestation. Serum concentrations of P4 fell dramatically before parturition, consistent with a role for this steroid in the regulation of gestational length. Male urine testing behavior was dearly cyclical, and maximal interest during the late interluteal period was followed by a rapid decrease with the onset of P4 secretion. These data provide the first substantive description of the hormonal milieu of the reproductive cycle, concurrent male behavior, and the serum hormonal patterns at the onset and termination of gestation in this endangered species.