Efficacy of oxfendazole against an ovine isolate of benzimidazole resistant Haemonchus contortus.

Eighteen parasite-free sheep were each infected with 6000 +/- 25 infective larvae of the AH-2, benzimidazole-resistant strain of Haemonchus contortus on each of experimental days -27, -15, -8 and -1. The sheep were subsequently randomized into 3 groups of 6 sheep each. Group 1 served as untreated controls; Groups 2 and 3 were treated orally with oxfendazole at dose levels of 5 mg/kg and 10 mg/kg body weight, respectively. At both dosage levels, oxfendazole was 100% effective against third, fourth, early fifth, and adult stages of the worms.