Evaluation of less than recommended dosages of levamisole phosphate for the treatment of gastrointestinal nematodes of cattle.

The anthelmintic activity of 3 dosages of injectable levamisole phosphate was evaluated in 84- to 145-kg calves from a herd of cattle with a history of heavy gastrointestinal nematode infections. Trichostrongylid egg counts in the calves varied from 450 to 700/g of feces. The anthelmintic was administered subcutaneously to 3 groups of 10 calves each, at the rate of 8 mg/kg of body weight (current manufacturer's recommendation), 6 mg/kg, and 4 mg/kg. A 4th group of 10 calves was utilized as untreated control calves. At necropsy, comparison of worm burdens between treated and untreated calves indicated apparent reductions (at 8 mg/kg, 6 mg/kg, and 4 mg/kg, respectively) for the various nematodes to be: Haemonchus placei adults-99.9, 100, and 98.3%; H placei L4-91.0, 94.0, 98.0%; O ostertagia late L4-93.8, 86.7, and 96.3%; Trichostrongylus axei adults-99.1, 100, and 100%; Cooperia spp adults-99.8, 99.5, and 99.5%; and Oesophagostomum radiatum adults-100, 100, and 100%. Statistical evaluation, by one-way analysis of variance, of the mean number of each species recovered showed significant (P less than 0.05) differences in the worm burdens between treated and untreated calves, but differences in efficacy between any 2 of the 3 drug dosages were not significant.