[Large-intestinal nematoda in bison]

In the Białowieza Forest the parasitological autopsy of large intestine of 6 bisons was made at the beginning of winter of 1987-1988, and 9 dissections were made in the latter part of both seasons. Four species of nematodes were found to occur together: Chabertia ovina, Oesophagostomum radiatum, Oe. venulosum and Trichocephalus ovis. At the end of wintering in bisons the invasion of Ch. ovina appeared in high percent of animals, but the intensity of it was low. However, the extensity and intensity of invasion of three remaining species of nematodes distinctly arose. In comparison with bisons in closed reserves, free living bisons assimilated Oe. venulosum and Ch. ovina. It is likely that the winter quarters are the source of invasion. It can be explained by the permanent accumulation of feaces with invasive forms of nematodes, and by feeding bisons on the great amount of hay, in which the invasive forms of nematodes may also occur.