Efficacy of doramectin injectable against Oestrus ovis and gastrointestinal nematodes in sheep in the southwestern region of France

A study was conducted to evaluate the therapeutic efficacy of doramectin ad ministered intramuscularly at a dose rate of 200 mug/kg to sheep harbouring naturally acquired infections of gastrointestinal nematodes and Oestrus ov is in the southwestern region of France. On day 0, 24 sheep were selected o n the basis of positive faecal egg counts (>100 EPG) and positive assessmen t of 0. ovis infection (including positive 0, ovis antibody level and posit ive clinical score). The sheep were randomly allocated to a non-medicated c ontrol group (T1) or a doramectin-treated group (T2) of 12 animals each. On day 0, sheep in group T2 received a single intramuscular injection of dora mectin (200 mug/kg), whereas those in group T1 received an intramuscular in jection of saline solution (sodium chloride, 0.02 ml/kg). Individual. faeca l egg counts were performed on days 0, 1, 2, 3, 4, 5, 6, 7, and 14. Between days 14 and 16, all sheep were slaughtered, and worm and O. ovis burdens w ere determined. In doramectin-treated sheep, faecal egg counts had decreased to zero by day 4 for all recovered types of nematode eggs: strongyles, Nematodirus sp., T richuris sp., and Rhabditidae sp. For strongyles, Nematodirus sp., and Rhab ditidae, the percentage reductions in faecal egg counts (geometric means) o f doramectin-treated sheep, compared to the non-medicated control sheep wer e 100% from days 4-7. For Trichuris sp., they were 100, 99.7, 99.9, and 100 % on days 4, 5, 6, and 7, respectively. On day 14, percentage reductions we re 100% for Nematodirus sp. and Rhabditidae, and 99.8 and 99.1% for strongy les and Trichuris sp., respectively. At necropsy, only adult nematodes and mainly first-stage 0. ovis larvae wer e recovered. Doramectin was highly efficacious against the adult stages of Teladorsagia circumcincta (100%), Nematodirus battus (100%), Nematodirus fi licollis (99.9%), Oesophagostomum venulosum (99.8%), and Trichuris sp. (99. 3%). It was also 100% efficacious against first-stage larvae of O, ovis. No abnormal clinical signs or adverse reactions in any of the sheep treated w ith doramectin were observed. (C) 2001 Elsevier Science B.V. All rights res erved.