Comparative efficacy of levamisole, thiabendazole and fenbendazole against cattle gastrointestinal nematodes

Efficacy of two older anthelmintics, levamisole and thiabendazole, was compared with a newer benzimidazole, fenbendazole, against naturally acquired gastrointestinal nematode infections in cattle superimposed with experimental infections of Bunostomum phlebotomum and Dictyocaulus viviparus. Twenty-four crossbred beef heifers of 7-9 months of age and 152 kg in average weight were randomly allocated to four groups of six calves. The cattle grazed on pastures contaminated with larvae of gastrointestinal nematodes and the lungworm for 2 months prior to Day 0. Treatment groups were as follows: Group 1--levamisole, topical at 10 mg kg-1; Group 2--thiabendazole paste at 110 mg kg-1; Group 3--fenbendazole paste at 10 mg kg-1; Group 4--untreated controls. All calves were necropsied for worm recovery between 8 and 10 days after treatment. Fecal egg/larval per gram counts at 18 and 42 h post-treatment indicated greatest reductions in Groups 1 and 2. By 7 days post-treatment, reduction in counts for all treated groups ranged from 99.1 to 100%, except for the 66.7% reduction of B. phlebotomum in Group 2. Seven nematode species were present in a sufficient number of untreated controls for valid efficacy assessment at necropsy. Efficacy of fenbendazole was 100% against all species, including Cooperia spp. L4 and immature (E5) D. viviparus. The overall efficacy of levamisole and thiabendazole was generally high (93.0-100% against Haemonchus placei adults, Cooperia punctata and C. spatulata adult males, Cooperia spp. adult females, Oesophogastomum radiatum, B. phlebotomum, and D. viviparus adults).(ABSTRACT TRUNCATED AT 250 WORDS)