Prophylactic efficacy of sustained-release ivermectin against induced nematode infestations in cattle.

The efficacy of sustained-release ivermectin was evaluated against challenge infestations of gastro-intestinal nematodes in a laboratory study involving 12 treated and 12 untreated control cattle. A weighted, orally administered osmotically activated device designed to lodge in the rumeno-reticulum and to deliver ivermectin at a dosage rate of approximately 8 mg/day for a 120-day period, was administered to treated cattle. Animals were challenged with infective larvae of Bunostomum phlebotomum and Oesophagostomum radiatum approximately 4 weeks, and with Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei and Cooperia pectinata approximately 4 and 6 weeks after bolus administration. No parasites were recovered from ivermectin-treated animals, representing 100% efficacy (p less than 0.01) against challenge infestations with larvae of all of the above species. Efficacy against an incidental infestation of Trichuris spp was 92% (p less than 0.01).