Albendazole, oxfendazole, fenbendazole, levamisole, closantel, ivermectin and febantel were administered to sheep on four farms and their efficacy assessed by faecal egg count reduction test. High level of resistance of Haemonchus contortus was found to benzimidazoles (albendazole, oxfendazole, fenbendazole) on all farms and to febantel on the one farm where it was tested. No resistance to closantel and levamisole was observed. Resistance to ivermectin was absent on the three farms examined under this study, but has been reported on the fourth farm in earlier work. It is concluded that anthelmintic resistance to benzimidazoles and the probenzimidazole, febantel, is a serious and widespread problem in H. contortus in sheep in Malaysia.
The anthelmintic efficacy of benzimidazoles, levamisole, closantel, ivermectin and moxidectin was evaluated on an institutional farm in Malaysia using faecal egg count reduction tests, controlled slaughter trials and an in vitro egg hatch assay. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles and ivermectin and of Trichostrongylus colubriformis against benzimidazoles and levaminsole on the same farm. Moxidectin was effective against the ivermectin resistant H. contortus.