Utility of serum progesterone and prolactin analysis for assessing reproductive status in the Asian elephant (Elephas maximus).
Concentrations of serum progesterone and prolactin were assessed during the perioestrous period and throughout gestation in the Asian elephant (Elephas maximus) as a means of generating information of potential use to managers. In > 95% of perioestrous periods (n=35), behavioural oestrus (as determined by bull interest, mounting and/or breeding) coincided with the onset of increased serum progesterone concentrations at the beginning of the luteal phase and continued through Day 7 (Day 1 = first significant serum progesterone rise). Within individuals, 1- to 2-day transient decreases (P < 0.05) in serum progesterone occurred between Days 2 and 9. Notably, no sexual behaviour was observed in any female after this transient fall in progesterone. Prolactin concentrations fluctuated randomly throughout the perioestrous period, with no clear pattern. During the study, four females conceived (one conceived twice), and two delivered three viable offspring. Serum progesterone was elevated above baseline throughout gestation, and then declined precipitously 2-3 days before parturition. Serum prolactin concentrations were significantly elevated above baseline (P < 0.05) after 5-6 months of gestation and remained high until after parturition. This study confirms that serum progesterone and prolactin analyses are useful tools for monitoring the reproductive status of Asian elephant females. Specifically, the transition from low to high progesterone secretion during the late interluteal/early luteal phase is predictive of oestrus and can be used to coordinate breeding efforts. Pregnancy can be confirmed by elevated serum prolactin after 6 months postbreeding, whereas the late gestational decrease in progesterone is predictive of impending parturition.