THE PREVALENCE OF ANTHELMINTIC RESISTANCE IN OVINE CASE SUBMISSIONS TO ANIMAL HEALTH LABORATORIES IN NEW-ZEALAND IN 1993

An analysis was undertaken of 177 veterinary diagnostic case submissio ns to two North Island and two South Island animal health laboratories for faecal egg count reduction testing in sheep during 1993 to provid e some comparative data on the frequency of occurrence of anthelmintic resistance. The results suggest that resistance to anthelmintics in s heep nematodes may be more common in the South Island than the North. In both instances this mainly involved resistance to a single drench t ype, the benzimidazoles. The data indicated a frequency of occurrence of resistance to benzimidazole anthelmintics of 61 and 72%, to levamis ole-type anthelmintics of 29 and 29% and to benzimidazole-levamisole c ombinations of 11 and 22% for submissions to North and South Island la boratories, respectively. In submissions from the South Island, resist ance to benzimidazoles involved infections of Nematodirus spp. alone m uch more frequently than those from the North.