EFFICACY OF DORAMECTIN IN THE PREVENTION OF GASTROINTESTINAL NEMATODEINFECTIONS IN GRAZING CATTLE

Two studies were performed to investigate the efficacy of doramectin i n the prevention of infection with Ostertagia ostertagi and Cooperia o ncophora in grazing calves. In each study, 24 parasite-naive calves we re randomly allotted to two equal groups and treated with either doram ectin at 200 mug kg-1 or saline prior to mid-season turnout (Day 0) on to contaminated pasture. Faecal egg counts were carried out twice week ly from 15 to 64 days after turnout and the cumulative faecal egg coun t was calculated for each group of calves. In the doramectin-treated a nimals, eggs first appeared in the faeces 19 days and 22 days later th an in controls for Studies 1 and 2, respectively. Mean cumulative faec al egg counts over the 64 days were reduced in the doramectin-treated groups by 71% and 87% for Studies 1 and 2, respectively (P < 0.01). Th e potential utility of injectable doramectin in the seasonal control o f gastrointestinal nematode infestations in relation to these findings is discussed.