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 she ep between 1986 and 1992 showed that 63% of them originated from prope rties carrying anthelmintic-resistant worms. Most of these cases invol ved resistance to a single drench type only, with the benzimidazoles b eing implicated most frequently. Overall, the figures suggested a freq uency of occurrence of resistance to benzimidazole anthelmintics of 74 %, to levamisole-type anthelmintics of 23% and to benzimidazole-levami sole combinations of 30%. No cases of resistance to milbemycin/avermec tin-type drenches were recorded.