154 REPRODUCTIVE SEASONALITY AND FOLLICULAR DYNAMICS IN THE PRZEWALSKI'S HORSE

Abstract

Artificial insemination has served as a valuable tool for the genetic management of small, isolated populations of several wildlife species (Pukazhenthi B et al. 2004 Development 16, 33–46). The overall aim of the present project was to develop a successful protocol for AI in the Przewalski horse (Equus ferus przewalskii), which is formally listed on the IUCN Red List as “extinct in the wild.” Achieving the long-term goal requires a series of requisite studies to improve our fundamental understanding of reproductive biology in this rare species of equid; therefore, our specific objectives in the present project were to (1) characterize ejaculate traits and examine the influence of seasonality in stallions; and (2) determine the follicular dynamics in mares. Stallions (n = 7) were anesthetized and subjected to a standardized electroejaculation procedure (Collins CW et al. 2006 Anim. Reprod. Sci. 94, 46–49). Testicular volume (TTV) and seminal traits [total sperm concentration (TSC), and total (TM) and progressive sperm motility (PM)] were assessed once each season (winter, January to March; spring, April to June; summer, July to September; fall, October to December) for 1 year, with data analyzed by repeated-measures ANOVA. Mares (n = 8) were examined by ultrasonography in a specialized chute system 3 days/week during breeding season (April to June) over 3 years. At each examination, ovarian structures [size of the dominant follicle and presence of corpora lutea (CL)] were assessed. Values for total ejaculate volume (mean ± SEM, 33.0 ± 22.2 mL), sperm motility (TM, 58 ± 19%; PM, 49 ± 18%), and TSC (2.8 ± 0.3 × 109) were highly variable among individuals. Seasonality significantly (P < 0.05) influenced TSC, which was highest in summer (4.41 ± 0.09 × 109) compared with spring (2.7 ± 0.5 × 109), fall (1.7 ± 0.4 × 109), and winter (2.5 ± 0.4 × 109). Season had no influence on TTV or other seminal traits (P > 0.05), with motile sperm being recovered at all ejaculation attempts. Ultrasonography revealed that the reproductive cycle of the Przewalski mare was composed of two phases. The follicular phase (4.3 ± 2.2 days; range, 3 to 7) was characterized by the presence of one dominant follicle that grew at a rate of 2.9 ± 0.2 mm (range, 1–6 mm) per day and ovulated at a size of 43.8 ± 1.5 mm in diameter (range, 30–57 mm). The luteal phase was distinguished by the presence of a CL that was sustained and evident on the ovary for 12.2 ± 3.3 days (range, 9–15) before regression. In summary, the basic reproductive physiology of the Przewalski horse is comparable with the domestic horse, including the ability of stallions to retain year-round spermatogenesis and ovarian follicular dynamics (including number, size, and growth rate) in the mare. These data allow us to suggest that established protocols for AI in the domestic horse (including estrus induction) likely will have relevance to adapting this technology to the genetic management of the rare Przewalski horse.

Morris Animal Foundation (Grant No. D07ZO-403), Sichel Endowment Fund, Smithsonian Endowment Fund, Animal Management staff at CRC and The Wilds.