Ultrasonography of the estrous cycle in female African elephants (Loxodonta africana)

The endocrinology of the elephant estrous cycle has been well characterized , but little emphasis has been placed on evaluating corresponding changes i n the reproductive tract. Ultrasound was used to document changes in reprod uctive tract morphology throughout the estrous cycle in four cycling female African elephants. During a 7-month period, frequent ultrasound examinatio ns (n = 190) during the luteal and non-luteal phase were compared with seru m progesterone and luteinizing hormone (LH) concentrations during a 7-month period. Ultrasonographic images documented vaginal and cervical edema and changes in mucus consistency during the non-luteal phase. The cross-section al diameter of the endometrium showed a dramatic increase during the non-lu teal phase and followed cyclic changes. A different pattern of follicular d evelopment on the ovary was associated with the two LH surges. Follicle gro wth associated with the first, anovulatory LH surge was characterized by th e formation of multiple small follicles, in contrast to the maturation of a single large follicle at the second, ovulatory LH (ovLH) surge. Ovulation and the subsequent formation of a corpus luteum (CL) were observed only aft er the ovLH surge. Ultrasound data in combination with endocrine assessment s suggest that the African elephant is non-ovulatory, although multiple non -ovulatory luteal structures developed during the late nonluteal phase of e ach cycle. Both ovulatory CL and non-ovulatory luteal structures were prese nt only through one cycle and regressed at the end of the luteal phase in c onjunction with the drop in serum progesterone. We conclude that periodic r eproductive-tract ultrasound assessments in association with continued endo crine monitoring of the estrous cycle should be incorporated into the routi ne reproductive health assessment of elephants. This information is necessa ry for determining reproductive fitness before making breeding recommendati ons. It also has proven to be an invaluable tool for use with assisted repr oductive techniques and has enormous potential for evaluating the efficienc y of hormonal therapies used to treat reproductive dysfunction. Zoo Biol 19 :369-382, 2000. (C) 2000 Wiley-Liss. Inc.