The anthelmintic efficacy of ivermectin in experimentally infected cattle

Abstract

The 22,23-dihydro derivative (ivermectin) of the major B 1 components of the avermectins was evaluated, by oral and parenteral routes, for anthelmintic activity in cattle experimentally infected with 7 gastro-intestinal nematode species and lungworm. Treatment at three dosage levels was administered when the parasites were in the L 4 developmental stage or when adult. The dosage expected to remove 95% of the nematodes (ED 95) by each route of administration against the various developmental stages of each species of parasite was calculated by methods of linear regression to choose dose levels to be used in subsequent developmental field trials. Parenterally, efficacy against L 4 stages of Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punctata, Oesophagostomum radiatum and Dictyocaulus viviparus exceeded 99% with treatment at 0.2 mg ivermectin/kg. Parenteral treatment of the adult parasites resulted in at least 98% reduction of worm burdens, except ≊ 90% for T. colubriformis, with 0.2 mg/kg. Oral treatment of L 4 stages of development with 0.2 mg/kg resulted in at least a 95% reduction in worm burdens of each of the 8 species of parasite. Oral treatment of the adult worms with 0.1 mg ivermectin/kg produced at least a 98% decrease in each parasite species, except for T. colubriformis (90% reduction) for which dose-response calculations suggest 95% efficacy with oral treatment at 0.2 mg/kg.