EFFICACY OF ORAL MOXIDECTIN AGAINST BENZIMIDAZOLE-RESISTANT ISOLATES OF GASTROINTESTINAL NEMATODES IN SHEEP

efficacy of orally administered moxidectin was determined against four benzimidazole-resistant nematode isolates. At the start of the trial, 30 lambs were each infected experimentally with 20,000 third stage la rvae (5000 Haemonchus contortus, 7000 Teladorsagia circumcincta, 3000 Trichostrongylus colubriformis and 5000 Cooperia curticei); 28 days la ter they were allocated randomly to three groups of 10: one untreated group, one group treated orally with fenbendazole (5 mg/kg bodyweight) and one group treated orally with moxidectin (0.2 mg/kg). Samples of faeces were taken five and 10 days after treatment and the lambs were killed 10 days after treatment. Fenbendazole reduced the average numbe r of nematode eggs in faeces by 95 per cent and the average number of worms by 25 to 45 per cent according to the species. The efficacy of m oxidectin against these benzimidazole-resistant isolates was 100 per c ent. No adverse reactions to either of the drugs were observed.