Evidence of benzimidazole resistance in Haemonchus contortus of sheep in north eastern zone of Tamil Nadu

Gastrointestinal nematode population in four unorganized sheep flocks of northeastern zone of Tamil Nadu were monitored for benzimidazole resistance using faecal egg count reduction test (FECRT), following oral administration of fenbendazole. The faecal egg count reduction obtained was 99, 70, 98 and 67% with a 95% lower confidence limit of 96, 50, 93 and 47 in the flocks of Tiruvallur, Vellore, Kancheepuram and Thiruvannamalai districts, respectively. Vellore and Kancheepuram flocks showed resistance whereas Tiruvallur and Thiruvannamalai flocks were susceptible to benzimidazole. Haemonchus contortus was the predominant nematode species present in coproculture.