Oral and injectable synthetic progestagens effectively manipulate the estrous cycle in the Przewalski's horse (Equus ferus przewalskii).

To date, there has been limited research on manipulation of the estrous cycle in endangered equids. The objectives of this study were to assess the efficacy of using combinations of: (a) oral altrenogest and PGF2α, and (b) injectable altrenogest and PGF2α for manipulation of ovarian activity in Przewalski's mares. Reproductive cycles were monitored by assessing follicular changes with rectal ultrasound and changes in urinary steroid hormones. In Study 1, five cycling mares were treated with oral altrenogest (n=11 cycles) for 14 days. In Study 2, cycling mares were treated with oral altrenogest for 12 days (n=5 cycles; n=5 mares) or a single injection of biorelease altrenogest (n=10 cycles; n=6 mares). In all study groups, PGF2α was given 2 days before cessation of progestagen treatment. In Study 1, mares responded in six of 11 cycles (54%) where treatment occurred with normal ovarian follicular development post hormone therapy. In Study 2, mares responded in four of five (80%, oral altrenogest) and eight of 10 (80%, injectable altrenogest) cycles with the development of an ovulatory follicle. With the use of injectable altrenogest, there was an obvious suppression of urinary estrogens and progetsagens. These results indicate that manipulation of the estrous cycle of Przewalski's mares can be achieved by administering oral (12 days) or injectable form of altrenogest in conjunction with PGF2α. Findings in the present study may have long term application for the development of timed artificial insemination as a genetic management tool for this critically endangered equid.

Abnormal reproductive patterns in Przewalski's mares are associated with a loss in gene diversity.

The ex situ population of the Przewalski's horse (Equus ferus przewalskii) is not self-sustaining (20% foaling rate), and the demography is skewed toward aging individuals with low gene diversity. We designed the present study to gain a better understanding of the reproductive biology of the Przewalski's mare and to determine whether age and gene diversity influenced reproductive function. Urine samples were collected 3-7 days/wk from 19 mares from May to September, and ultrasound examinations of follicular structures were performed 3 days/wk for 5 wk from May through July in nine individuals. A high proportion of mares exhibited abnormal (endocrine, 5 [26.3%] of 19; follicular, 2 [22.2%] of 9) or acyclic (endocrine, 4 [21.1%] of 19; follicular, 3 [33.3%] of 9) reproductive patterns. In four cyclic mares, estrous cycle length was 25.1 ± 1.2 days, with 12.2 ± 0.9 days of diestrus. Follicles in cyclic mares grew 1.2 ± 0.6 mm per day and ovulated after reaching 40.4 ± 8.9 mm. Mares with a high coefficient of inbreeding excreted reduced levels of mean urinary estrogens (r(2) = 0.476, P < 0.05), but age had no significant impact on reproductive patterns in this population. Overall, these data suggest that long-term genetic management of this population is necessary to maintain reproductive fitness.