2012 Volume 17 Issue 3 Pages 97-109
The combination of a few factors, including poor captive reproduction, secession of importation from the wild, advances in hormone detection and ultrasonography, and, regrettably, elephant culling in Africa, has contributed to the current knowledge on the elephant cycle. Several reproductive features in elephants differ markedly from other mammals. These include the urogenital tract anatomy, length and structure of the cycle, the formation of multiple corpora lutea and the type and secretion pattern of reproductive hormones. Being 12 to 18 weeks in length, the elephant estrous cycle is the longest amongst all studied non-seasonal mammals to date. Progesterone rises one to three days after ovulation, indicating the start of the luteal phase, which lasts six to 12 weeks. This is followed by a four to six weeks follicular phase that is concluded by two, precisely spaced and timed, LH surges. In general, the first, anovulatory LH surge occurs exactly 19 to 21 days before the second, ovulatory surge. Normally, a single follicle is ovulated. However, beside a corpus luteum (CL) forming on the site of ovulation, multiple accessory CLs can be found on the ovaries. Unlike many other species, the predominant progestagen secreted by luteal tissues is not progesterone, but rather its 5-α-reduced metabolites. The currently known aspects of the unique estrous cycle in Asian and African elephants, covering estrous behavior, circulating hormones, ultrasonography and anatomy of the reproductive organs and its pathology as well as hormonal manipulation treatment possibilities, will be reviewed here.