Submission Number: CHE-4-23-2

Abstract Number: 177

EFFECTS OF PROSTAGLANDIN F₂ ON OVARIAN CYCLE DYNAMICS IN ADDAX, ADDAX NASOMACULATUS.

Cheryl S Asa* ¹, KL Bauman ¹, MT Fischer ¹, JE Bauman ¹, EW Houston ¹ and BW Read ^1,2

St. Louis Zoo, St. Louis, MO, USA ¹
Disney's Wild Animal Kingdom, Lake Buena Vista, FL, USA ²

Abstract:
Female addax (an endangered antelope) can experience periods of anovulation during which follicular activity continues, although levels of estradiol continue to fluctuate within the follicular phase range. Anovulatory periods vary in length, are not related to presence of a male, and end spontaneously. To begin elucidating the mechanism(s) controlling ovulation in this species, the response of the corpus luteum to administration of prostaglandin F₂ (PGF) was assessed, since release of the dominant follicle from progesterone suppression results in ovulation in domestic bovids. Six mature female addax (aged 4 to 11 yr) were given two 25-mg doses of PGF 11 days apart, and serum progesterone and estradiol were assayed to monitor activity of corpora lutea and follicles, respectively. PGF successfully lysed corpora lutea in all cases, judged by return to baseline (<2 ng/ml) of progesterone. Latency to ovulation (i.e., first increase in progesterone) following CL lysis ranged from nine to 117 days. However, two females did not ovulate at all in the several weeks before or four months following treatment. Thus, it appears that in addax progesterone may well suppress final growth of the dominant follicle and prevent ovulation, but removal of this progesterone suppression does not reliably lead to ovulation. Progesterone withdrawal, therefore, seems necessary but not sufficient for ovulation in the addax. The proximate mechanism for control of LH and ovulation is still unclear. Although addax can reproduce throughout the year in captivity, in their natural range in northern Africa a seasonal pattern in reproduction has been reported. Our studies have been conducted primarily during the months that would be considered their non-breeding season in the wild. The pattern seen may be best compared to the shallow anestrus described for some domestic hoofstock. However, photoperiodic control is not likely, since, compared to U.S. latitudes, their natural range is significantly closer to the equator where changes in daylength are less, not more, pronounced. Limited food or water or extremes in temperature, factors mitigated in captivity, are possible natural modulators.

Keywords: ovulation, prostaglandin, addax, corpus luteum,seasonal reproduction

This abstract is being presented at: 8:00 AM in session:
Ovulation