Understanding the Reproductive Biology of the Przewalski's Horse (Equus ferus przewalskii)

Abstract

The Przewalski's horse (Equus ferus przewalskii) once roamed the Eurasian Steppe but is now considered Critically Endangered with only 1872 individuals remaining in the world, representing progeny from only 14 founder animals (Lee and Boyd, 2008). Genetic diversity needs to be optimal for long term survival of this species. Unfortunately, increasing genetic diversity of the captive population in North America has been hindered by a decrease in fertility. Therefore, the main focus of this research was to characterize reproductive parameters in Przewalski's horse, including estrus cycle in mares and seminal traits in stallions, and determining whether age or inbreeding had an impact on these traits. A secondary focus was to determine whether hormone manipulation of the estrous cycle in mares could be utilized for the long-term goal of using artificial insemination as a breeding management tool for this species. To facilitate these studies, a technique for palpation of Przewalski's mares was developed; the first application of such a procedure in a wild equid. Subsequently, we were able to describe follicular changes in relation to urinary hormone patterns. Fifty percent of the mares had either irregular or acyclic hormonal and follicular patterns. These patterns were directly correlated with inbreeding which is the first time such a correlation has been described in this species. Estrous manipulation was possible using an injectable biorelease form of the progestagen, altrenogest. In stallions, we developed a reliable method of semen collection for Przewalski's stallions and, as a result, describe seminal traits from 98 semen collections from 14 stallions. Based on these collections, we were able to show that sub-fertility in this population could be due to the low percentage of normal spermatozoa. Based on variable analysis, seminal traits total concentration, volume and morphology showed variable changes through the year. Traits also varied on an individual stallion basis. Together, these studies demonstrated that inbreeding is detrimentally affecting the reproductive fitness of this species and that aggressive management is needed for long term sustainability of the captive population.