Evaluation of fenbendazole as an anthelmintic for gastrointestinal nematodes of cattle.

Calves naturally infected with Ostertagia, Haemonchus, Trichostrongylus, and Cooperia were used in a controlled experiment to determine the anthelmintic efficacy of fenbendazole, methyl-5-(phenylthio)-2-benzimidazolecarbamate, and to compare this with the efficacy of levamisole. The calves were placed in dry lots for approximately 3 weeks, ensuring that immature Ostertagia larvae were in arrested development before the calves were treated. In calves given doses of 8 mg of levamisole/kg of body weight and 5 and 7.5 mg of fenbendazole/kg, reductions of adult Ostertagia were 95%, 99%, and 99% respectively. Reductions of developing Ostertagia L4 were 29%, 99%, and 100%; of arrested Ostertagia L4--5%, 24%, and 72%; of adult Haemonchus--97%, 100%, and 100%; of adult Trichostrongylus--97%, 99%, and 100%, and of adult Cooperia--100%, 100%, and 100%--as compared with data in untreated controls.