Control of gastrointestinal nematodes in first season grazing calves by two strategic treatments with eprinomectin

A study was carried out to evaluate the effects of strategic early-season t reatments with eprinomectin on first-season grazing calves exposed to stron gyle infections on a naturally contaminated pasture. Two groups of first gr azing season (FGS) calves were turned out in mid-May on two plots that were similar with respect to size and herbage infectivity. They grazed separate ly until housing at the end of October. One of these groups was given eprin omectin pour-on at turnout and 8 weeks later, while the ether group served as untreated controls. The results showed that the treatments reduced gastr ointestinal strongyle infections throughout the season as evidenced by lowe r faecal egg counts and serum pepsinogen levels compared with the controls. Furthermore, the results of herbage larval counts and postmortem worm coun ts in tracer animals demonstrated that the treatment had reduced herbage in fectivity on the 'treated' plot. Finally, the chemoprophylactically treated calves had a better weight gain over the duration of the study than the un treated controls. (C) 2000 Elsevier Science B.V. All rights reserved.