Journal of Veterinary Parasitology

Sixteen flocks of sheep from unorganized sector of eight districts (five in eastern and three in western region) in Haryana were selected to study the prevalence of resistance in gastrointestinal (GI) nematodes to commonly used anthelmintics, tetramisole (15 mg kg⁻¹) and fenbendazole (5 mg kg⁻¹) by faecal egg count reduction test (FECRT). Reduction in faecal egg count was ≥ 95% in 33.3%, 16.7% and 23.1% flocks of sheep treated with tetramisole, morantel and fenbendazole, respectively. Further analysis revealed resistance in Haemonchus contorlus to the oral doses of tetramisole, morantel tartrate and fenbendazole in 66.7%, 83.3% and 76.9% flocks, respectively. This study shows that resistance in the most pathogenic and dominant parasite, H. contorlus, is spreading fast against the commonly used anthelmintics in sheep of unorganized farms of Haryana. This problem needs to be tackled with the judicious use of available anthelmintics.