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

Abstract

The endocrinology of the elephant estrous cycle has been well characterized, but little emphasis has been placed on evaluating corresponding changes in the reproductive tract. Ultrasound was used to document changes in reproductive tract morphology throughout the estrous cycle in four cycling female African elephants. During a 7‐month period, frequent ultrasound examinations (n = 190) during the luteal and non‐luteal phase were compared with serum 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‐sectional diameter of the endometrium showed a dramatic increase during the non‐luteal phase and followed cyclic changes. A different pattern of follicular development on the ovary was associated with the two LH surges. Follicle growth associated with the first, anovulatory LH surge was characterized by the 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 after the ovLH surge. Ultrasound data in combination with endocrine assessments suggest that the African elephant is non‐ovulatory, although multiple non‐ovulatory luteal structures developed during the late non‐luteal phase of each cycle. Both ovulatory CL and non‐ovulatory luteal structures were present only through one cycle and regressed at the end of the luteal phase in conjunction with the drop in serum progesterone. We conclude that periodic reproductive‐tract ultrasound assessments in association with continued endocrine monitoring of the estrous cycle should be incorporated into the routine reproductive health assessment of elephants. This information is necessary for determining reproductive fitness before making breeding recommendations. It also has proven to be an invaluable tool for use with assisted reproductive techniques and has enormous potential for evaluating the efficiency of hormonal therapies used to treat reproductive dysfunction. Zoo Biol 19:369–382, 2000. © 2000 Wiley‐Liss, Inc.

Luteogenesis during the estrous cycle in Asian elephants (Elephas maximus)

“…During the follicular phase in African elephants, the occurrence of two follicular waves, each terminated by an LH peak, has been previously reported (Hermes et al 2000). The authors hypothesized that the first LH peak induced luteinization of subordinate follicles from the first wave.…”

“…Our measurements of CLs in cycling Asian elephants did not exceed 4.1 cm. Similarly, in nonpregnant African elephants, Hanks & Short (1972) reported cyclical CL sizes of 2.4-3.3 cm in culled animals while Hermes et al (2000) reported an average diameter of 2.58G0.45 cm (range: 2.3-3.8 cm) for CLs observed by ultrasound. This suggests that CLs are significantly larger during gestation than during the cycle.…”

“…Histological interpretation of CL origin is difficult. The finding of so called 'ovulation stigmata' (trauma of ovulation) in more than one CL (Perry 1953, Hanks & Short 1972, Smith & Buss 1975 disagrees with both the generally accepted fact that elephants are monovular as well as ultrasound observations of only a single ovulation per cycle in this and in other reports (Hermes et al 2000, Hildebrandt et al 2000a). This suggests that there is a different reason for the origin of these stigma-like appearing protuberances.…”

“…The technological advances of transrectal ultrasonography have been a major breakthrough, enabling us to depict and follow the ongoing physiological ovarian process over time in elephants (Hermes et al 2000, Hildebrandt et al 2000a, 2000b. The first sequential ultrasound study which was performed in African elephants focused on the interluteal phase and demonstrated that multiple CLs were formed in every cycle (and not only during pregnancy; Hermes et al 2000). It was suggested that these CLs were derived either from nonovulatory LUFs forming acCLs or after ovulation.…”

“…Luteal tissue undoubtedly is crucial for pregnancy maintenance, but despite determined research efforts, the factors controlling CL formation and function in elephants have remained elusive (Hodges et al 1994, Allen 2006. The technological advances of transrectal ultrasonography have been a major breakthrough, enabling us to depict and follow the ongoing physiological ovarian process over time in elephants (Hermes et al 2000, Hildebrandt et al 2000a, 2000b. The first sequential ultrasound study which was performed in African elephants focused on the interluteal phase and demonstrated that multiple CLs were formed in every cycle (and not only during pregnancy; Hermes et al 2000).…”