Comparative efficacy of fenbendazole, dichlorvos, and levamisole HCI against gastrointestinal nematodes of pigs.

Forty-two weanling pigs raised under similar management conditions were used to compare the effectiveness of fenbendazole, dichlorvos, and levamisole HCl against Oesophagostomum dentatum, O. quadrispinulatum, Ascaris suum, Trichuris suis, Hyostrongylus rubidus, and Strongyloides ransomi. All three drugs were given in the feed. Eleven pigs served as unmedicated controls; 11 pigs received fenbendazole (3 mg/kg) on days 1, 2, and 3; 10 pigs received dichlorvos (17 mg/kg) on day 3; and 10 pigs received levamisole HCl (8 mg/kg) on day 3. Fecal specimens from all 11 pigs were collected before and after anthelmintic treatment and examined for nematode eggs. All pigs were killed on day 7, and residual nematodes were counted. The calculated efficacies against the above species, respectively, were: fenbendazole, 99.9, 100, 92.4, 66.0, 99.9, and 0%; dichlorvos, 99.4, 99.9, 100, 99.9, 99.9, and 86.9%; levamisole HCl, 97.1, 99.7, 97.9, 26.1, 94.4, and 99.9%.