The efficacy of in-feed medication with fenbendazole against gastrointestinal nematodes of sheep, with particular reference to inhibited larvae.

Anthelmintic activity of fenbendazole in a feed formulation was tested against nematode parasites of sheep. Dose rates ranging from 1.4 mg per kg for four days to 0.4 mg per kg for 14 days removed 98 to 100 per cent of the total gastrointestinal worm burden, including large numbers of inhibited fourth stage larvae of Ostertagia circumcincta. One hundred per cent effectiveness against adult Dictyocaulus filaria was also recorded.