Efficacy of orally administered moxidectin against naturally acquired gastrointestinal nematodes in cattle.

Anthelmintic efficacy of moxidectin, an experimental antiparasitic macrocyclic lactone, was evaluated in a group of 15 calves harboring naturally acquired gastrointestinal nematodes. Three groups of 5 calves each served as untreated controls (group 1) or principals that were given moxidectin PO at the rate of 0.2 mg/kg (group 2) or 0.4 mg/kg (group 3) of body weight. Equal numbers of control and treated calves were necropsied for parasite recovery on days 10 (3 control and 3 of each treatment group) and 11 (2 control and 2 of each treatment group) after treatment. Efficacies at both doses were greater than 99.8 and 99.9% against active and inhibited larvae and adults of Ostertagia spp, respectively. The overall mean efficacy of each dose was greater than 99.9%.