EN
The paper presents different aspects of natural gastrointestinal nematode infection in this primitive, prolific Polish Wrzosówka breed of sheep. The study was carried out on the flock located at the farm run by Warsaw Agricultural University at Żelazna (central Poland) in 1995-1998. Egg counts per gram of faeces, larval differentiation, total white blood cell counts, blood eosinophil counts, interleukin-5 concentration, lymphocyte blastogenic activity and IgG immune response were discussed. The egg counts were overdispersed and followed a different pattem each grazing season. The larvae obtained from faecal culture belonged to 6 categories: Trichostrongylus spp., Haemonchus contortus, Teladorsagia spp., Cooperia spp., Chabertia ovina/Oesophagostomum spp. and Nematodirus spp. However there were no discemible pattems in the com position of nematode population over time. Data analyses have shown that egg counts, eosinophil counts, IL-5 concentration and IgG level in different months each year were repeatable. The results obtained in two divergent groups of sheep, chosen for consistently low or high faecal egg counts have been presented also. Polish Wrzosówka breed of sheep is under conservation breeding program based mainly on the markers of breed standard. The results obtained in this study revealed that some parasitological, haematological and immunological parameters should be added to this program.