THE ANTHELMINTIC EFFICIENCY OF LAEVO‐TETRAMISOLE HYDROCHLORIDE AGAINST NEMATODE PARASITES OF SHEEP AND CATTLE

Summary Critical anthelmintic tests and controlled trials were used to assess the efficiency of laevo‐tetramisole hydrochloride against nematode infections in sheep and cattle. In sheep, oral dose rates of 5 mg/kg and above were 94 to 100% effective against adult Haemonchus contortus, intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbianum, O. venulosum and Chabertia ovina. A dose rate of 7.5 mg/kg was required for consistently high activity against Ostertagia spp, but activity against Trichostrongylus axei remained variable at this dose level. Efficiency against Trichuris ovis ranged from 76 to 100% at a dose rate of 10 mg/kg. The drug was 94 to 100% effective against 7‐day old and 14‐day old H. contortus, intestinal Trichostrongylus spp and O. colun bianum infections, and 83 to 89% effective against 14‐day old Ostertagia spp and T. axei, at a dose rate of 5 mg/kg. Seven‐day old Ostertagia spp larvae were highly resistant at a dose rate of 10 mg/kg, while activity against T. axei infections of the same age appeared variable at 5 and 10 mg/kg. In cattle, subcutaneous treatment at dose rates of 1.5 mg/kg and above, and oral treatment at 7.5 mg/kg, were 93 to 100% effective against adult Haemonchus placei, intestinal Trichostrongylus spp, Nematodirus helvetianus, Cooperia spp and Oesophagostomum radiatum, and 84 to 98% effective against Ostertagia ostertagi. Against Trichostrongylus axei, a rate of 5 mg/kg subcutaneously was 83% effective, and a rate of 7.5 mg/kg orally 97% effective, while these dose rates gave 88 to 100% clearance of adult Dictyocaulus viviparous.