EFFICACY OF DORAMECTIN FOR TREATMENT OF EXPERIMENTALLY-INDUCED INFECTION WITH GASTROINTESTINAL NEMATODES IN CALVES

Objective-To determine the efficacy of injectable doramectin against e xperimentally induced infections with adult and larval (L(4)) stages o f gastrointestinal nematodes in calves. Procedures-In each experiment, between 20 (experiments 1 and 2) and 30 (experiment 3) parasite-free yearling calves were selected and allotted to groups of 10/group. All calves received oral inoculation of the following infective larval sta ges of these nematode species: Cooperia onchophora, C punctata, C zurn abada, Cooperia spp, Haemonchus placer; Nematodirus helvetianus, Oesop hagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axel, and T colubriformis. Infections or treatments were timed so that, by day o f treatment, the population of each parasite species had matured to th e stage to be tested (adult or L(4)). On day of treatment, calves rece ived doramectin (200 mu g/kg of body weight, SC), and infected nonmedi cated control calves received saline solution SC at the same time. All calves were slaughtered at least 14 days after treatment.Results-Effi cacy against the following adult and L(4) species was 2 99%: C onchoph ora, C punctata, C zurnabada, Cooperia spp, H placei; Oes radiatum, O ostertagi, and T colubriformis. Doramectin was also 100% efficacious a gainst the L(4) stage of T axei. Efficacy against the adult and L(4) s tages of N helvetianus was 9.6 and 77.4 to 83.3%, respectively. Conclu sions-Doramectin, at a dosage of 200 mu g/kg, is effective in controll ing the prevalent gastrointestinal nematodes (adult and L(4) stages) f ound in naturally infected calves. Clinical Relevance-Doramectin, a ne w anthelmintic, was effective against recent field strains of the most prevalent gastrointestinal parasites found in cattle in the United St ates, and could provide another alternative for control of these paras ites.