COMPARATIVE FIELD-EVALUATION OF DIVIDED-DOSING AND REDUCED FEED-INTAKE UPON TREATMENT EFFICACY AGAINST RESISTANT ISOLATES OF TELADORSAGIA CIRCUMCINCTA IN SHEEP AND GOATS

The effects of modifying drug administration and food intake upon the efficacy of fenbendazole against resistant isolates of Teladorsagia (O stertagia) circumcincta were investigated using naturally infected she ep and goats. Administration of the manufacturer's recommended dose (M RD) as two 2.5 mg kg(-1) bodyweight doses divided by a 12-hour interva l resulted in an apparent increase in efficacy of over 28 per cent com pared with conventionally treated sheep. Withholding feed for 24 hours before treatment at the MRD resulted in respective increases of 39.7 per cent (P<0.05) and 25.2 per cent compared with conventionally treat ed sheep and goats. A combination of food withdrawal and divided dosin g did not further increase treatment efficacy in goats. It is suggeste d that withholding feed, divided-dosing or combining these methods may extend the useful life of the broad spectrum class of anthelmintics.