Reduced activity of levamisole against Ostertagia ostertagi in dairy calves

Levamisole bolus formulation was administered in single doses, at rates of 5.8 to 8.1 mg/kg body weight, in 3 controlled tests in male dairy calves (n = 22) in Kentucky. Removals of natural infections of adult Ostertagia ostertagi were 70% and 76% for calves from a hear with a history of regular treatments with levamisole and 85% for calves from a herd receiving levamisole occasionally. Activity against other abomasal nematodes and lungworms was also evaluated.