THE OCCURRENCE OF ANTHELMINTIC-RESISTANT SHEEP NEMATODES IN THE SOUTHERN NORTH-ISLAND OF NEW-ZEALAND

An analysis of veterinary diagnostic cases submitted to the Batchelar Animal Health Laboratory for faecal egg count reduction testing in sheep between 1986 and 1992 showed that 63% of them originated from properties carrying anthelmintic-resistant worms. Most of these cases involved resistance to a single drench type only, with the benzimidazoles being implicated most frequently. Overall, the figures suggested a frequency of occurrence of resistance to benzimidazole anthelmintics of 74%, to levamisole-type anthelmintics of 23% and to benzimidazole-levamisole combinations of 30%. No cases of resistance to milbemycin/avermectin-type drenches were recorded.