USE OF A PROPHYLACTIC DORAMECTIN PROGRAM TO CONTROL SUBCLINICAL PARASITIC GASTROENTERITIS IN CALVES IN COUNTY CLARE

A field trial was conducted on a commercial farm in County Clare. Two groups of twelve calves were grazed on similar and adjacent paddocks, one group was protected against parasitic gastroenteritis (pge) by two subcutaneous infections of 200 mcg/kg of doramectin, a novel avermect in, on the day of turnout and 56 days later; the other group was untre ated. Measurements were made of bodyweight, faecal egg count, plasma p epsinogen concentrations, worm burdens at necropsy after housing, and of pasture larvae both by herbage sampling and by the exposure of trac er calves. The results indicated that there was only a moderate level of challenge on the pasture, but that the two doramectin treatments pr evented the treated animals suffering from subclinical parasitic gastr oenteritis. The untreated animals steadily accumulated worms from the pasture, as indicated by increased faecal egg counts, decreased livewe ight gain and modest elevations in their plasma pepsinogen concentrati ons. By the end of the 179-day grazing season the treated animals had outperformed the controls by a mean of 21kg.