CONTROL OF GASTROINTESTINAL TRICHOSTRONGYLES WITH A SINGLE APPLICATION OF DORAMECTIN POUR-ON AT TURN-OUT IN 2ND-SEASON BEEF-CATTLE

Two studies were conducted in France in 1996 to investigate the effica cy of a single application of doramectin pour-on, at turn-out, in cont rolling parasitic gastro-enteritis (PGE) in second-season grazing catt le. Treated animals were compared to control animals grazed on separat e but similar pastures. Control animals were treated, according to nor mal farm practice, at mid-season with a short acting anthelmintic drug . Weight gain, faecal egg counts, coprocultures, herbage larval counts , serum pepsinogen concentrations and antibody levels were used as par ameters. In one study, doramectin treatment resulted in lower infectio n levels during the first part of the grazing season. No difference in infection level could be detected in the second part of the Study and no clinical signs of PGE were seen in either group. However, doramect in-treated cattle showed a weight gain advantage steadily increasing f rom Day 28 to finally reach 38 kg (P less than or equal to 0.05) at ho using. In the second study, increasing infection levels following turn -out resulted in PGE, on Day 84, in the control group. The doramectin treatment prevented clinical parasitism and a better weight gain of 19 kg (P less than or equal to 0.05) was recorded, on Day 84, for dorame ctin-treated heifers. In the second part of the grazing season, infect ion levels were comparable between both groups. The weight gain differ ence observed between groups on Day 84 showed a tendency to persist at a non significant level of 11 kg up to the end of the grazing season.