Comparative efficacy of five anthelmintics against trichostrongylid nematodes in sheep

The efficacy of levamisole, ivermectin and three different preparations of oxfendazole, applied at the recommended rate, were evaluated in flocks of sheep kept at two farms in Thal desert, Pakistan. Sixty animals on each farm were selected randomly on the basis of their weight and egg count of more than 150 eggs per gram of faeces. Three preparations of oxfendazole (fendamex, oxazole, syatamex), levamisole and ivermectin were given to five groups while one untreated group was kept as control. Faecal egg counts, faecal egg count reduction test, postmortem worm count and copro-culture were performed to assess the efficacy of selected anthelmintics. Levamisole and ivermectin preparations reduced (P less than or equal to 0.05) prevalent species of gastrointestinal nematodes in both flocks. Oxfendazole preparations exhibited low efficacy and some gastrointestinal nematodes (Haemonchus and Trichostrongylus) were suspected for resistance against these preparations, with resistance more pronounced in oxazole followed by systamex and fendamex. It was concluded that all oxfendazole preparations had low efficacy with suspicion for anthelmintic resistance while levamisole and ivermectin had reasonable effectiveness against prevalent gastrointestinal nematodes of sheep kept in Thal desert, Pakistan.