Temporary ovarian inactivity in elephants: relationship to status and time outside.
The captive elephant population in North America is in reproductive decline and, without importation from the wild, may cease to be viable within the next several decades. The estrous cycle of three captive, reproductive-age African elephants was monitored for 3 years by measuring serum progesterone concentrations. Each elephant experienced one or more episodes of extended low progesterone (>12 weeks), analogous to supposed terminal cessation of estrous cyclicity or 'flatlining' that has been described in some captive Asian and African elephants. Other studies have reported lengthy non-luteal (follicular) phases that indicate extended episodes of ovarian inactivity; however, this phenomenon has not been examined in detail. In this study, total duration of temporary ovarian inactivity or acyclicity followed a social rank pattern, with the most subordinate female having the longest and the dominant female the shortest duration. During periods of acyclicity, the number of hours the elephants spent outside was significantly less than during non-luteal or luteal phases of the cycle. Except in one instance, behavioral data recorded by elephant keepers during their interactions with the elephants showed no change in handling during periods of ovarian inactivity. Further study is necessary to distinguish the causative agent for temporary cessation of estrous cyclicity. Understanding this phenomenon is imperative for the future reproductive viability of captive elephant populations.