Resistance of sheep from different genetic groups to gastrointestinal nematodes in the state of São Paulo, Brazil

Abstract Infections by gastrointestinal nematodes cause large losses to sheep breeders. In the study reported here, the resistance to gastrointestinal nematodes was analyzed in sheep of adapted and non-adapted breeds, maintained in naturally infected pastures. A total of 134 females from seven genetic groups were monitored during 20 months: Santa Ines (OSI), Dorper (ODO), Texel (OTX), Ile de France (OIF), and animals from crosses of Santa Ines ewes with Dorper (ODS), Texel (OTS) and Ile de France (OIS) rams. Blood samples were collected monthly to determine the packed cell volume (PCV), and feces were collected at the same time to count the eggs per gram (fecal egg counts = FEC) and identify the genera of the prevalent parasites. The statistical analyses of the data showed significant differences ( p p Haemonchus spp. (85.6%), followed by Trichostrongylus spp. (10.8%), Oesophagostomum spp. (2.9%) and Cooperia spp. (0.7%). The results obtained in this study show that the crossing of the Texel and Santa Ines breeds can be considered an alternative for sheep production in the Southeast region of Brazil due to the lower egg output by gastrointestinal nematodes.