The Przewalskis horse (Equus caballus przewalskii) became extinct in the wild during the 1960s. Based on a successful captive breeding program with 13 founder individuals, Przewalskis horse was reintroduced to the Greater Gobi Part B Strictly Protected Area (SPA) in SW Mongolia in the late 1990s.
The Asiatic wild ass (E. hemionus hemionus), Przewalskis horse and sometimes domestic horses live sympatricly in the Gobi B SPA. Previously published data demonstrates that these equids select for different resources. As a result of their different requirements and utilization of the parks resources, their home-range size and social structure differs. Asiatic wild asses live in fission-fusion groups, with recorded group sizes up to 1000 individuals and have a 10 times larger home range than the Przewalskis horses, which live in well structured and stable harem groups or bachelor-groups. Parasitological examinations in the three equid species show how the factors home range, social structure and resource selection significantly impact the parasitic burden. Asiatic wild asses are potentially exposed to a higher risk of parasite re-infection, due to their temporal aggregation in very large groups. This study demonstrates a highly significant greater parasite load in the Asiatic wild ass for the majority of parasites (Dictyocaulus arnfieldi, Trichostrongylus axei, Strongyloides westeri, Parascaris equorum), compared to Przewalskis horses and domestic horses in the same habitat. Only for eggs of strongylids, eggs of anoplocephalidae and Eimeria leuckarti, domestic horses had a higher load. The potential risk of cross infection between sympatric living equids is high, as is the cross infection between ruminants and equids. Furthermore, this study reports for the first time the occurrence of lungworms in free ranging Przewalskis horses. Whereas, Asiatic wild asses and Przewalskis horses seem to cope very well with the sometimes high parasite burden, Mongolian domestic horses manifested typical parasite-burden symptoms.
Przewalskis horse, Asiatic wild ass, Mongolian domestic horse, parasites, sympatric, cross-infection, home range