Response of resistant and susceptible Brazilian Somalis crossbreed sheep naturally infected by Haemonchus contortus

This study was carried out to evaluate the performance of Brazilian Somalis sheep to natural infections by gastrointestinal nematodes. During 98 days, 75 weaned sheep, initially 3–4 months old, were kept on the same pasture and evaluated. Fecal and blood samples were collected for parasitological and hematological exams. After this period, the eight most resistant and the eight most susceptible animals were selected based on their individual averages of nematode fecal egg counts and were slaughtered for worm burden determination and nematodes identification. Abomasum and abomasum lymph nodes were also recovered for gene expression analysis. The animals selected as resistant had lower fecal egg counts during experimental period and smaller worm burdens than the susceptible ones (P