Nematode control practices and anthelmintic resistance on British sheep farms.

Nearly 23 per cent of 3000 randomly selected sheep farmers returned questionnaires on strategies to control the development of anthelmintic resistance. Twenty-five per cent stated that they regularly checked the accuracy of their drenching gun, and 52 per cent stated that they weighed a few animals and treated the whole flock like the heaviest. The mean annual frequency of dosing lambs was 4.39 compared with 2.43 for ewes. Forty-eight per cent stated that they changed the anthelmintic group annually. Seventeen per cent always treated sheep brought on to their farm with ivermectin. However, only 7 per cent had had their flocks tested for anthelmintic-resistant nematodes. The responses suggest that most sheep farmers are not actively seeking to prevent the development and spread of anthelmintic-resistant nematodes.