CRITICAL AND CONTROLLED LABORATORY TRIALS IN SHEEP WITH TETRAMISOLE

Summary Critical and controlled anthelmintic tests were carried out using tetramisole hydrochloride per os against adult and immature gastro‐entestinal nematodes of sheep. The drug was highly effective against adult Haemonchus contortus, Ostertagia spp, Trichostrongylus axei, intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbi‐anum and Chabertia ovina, and against 5th stage worms of the two latter species, at 10 mg/kg bodyweight and above. Efficiency against Trichuris ovis ranged from 67 to 100% at 20 mg/kg. A dose rate of 10 mg/kg was 98 to 100% effective against 14‐day old H. contortus and T. axei, and against both 7‐day and 14‐day old intestinal Trichostrongylus spp infections, but a rate of 15 mg/kg was required for high activity against 14‐day old Ostertagia spp. Seven‐day old infections of H. contortus, T. axei and particularly Ostertagia spp were more resistant, and drug activity was variable at a dose rate of 15 mg/kg. Tetramisole would appear to have good activity against 7‐day and 14‐day old larvae of O. columbianum at 15 mg/kg in lambs in which the development of this species tended to be retarded.