Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand

Abstract

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random sample of beef cattle herds in the North Island of New Zealand. METHODS: A cross-sectional prevalence study was conductedusing a standardised faecal nematode egg count (FEC) reduction(FECR) test (FECRT) for ivermectin, levamisole and albendazoleon 60 calves on each of 62 farms in the North Islandchosen at random from farms that conformed with the selectioncriteria. Resistance to an anthelmintic was inferred when therewas <95% reduction in FEC 7-10 days after treatment. Larvalcultures were performed for all control groups and for treatedgroups for which resistance was evident. RESULTS: Of the farms that completed the FECRT, 4/61 (7%)showed ≥95% reduction in FEC for all anthelmintics tested.Resistance to ivermectin was evident on 56/61 (92%) farms,to albendazole on 47/62 (76%) farms, and to both ivermectinand albendazole on 45/61 (74%) farms. Resistance to levamisolewas evident on only 4/62 (6%) farms. The parasites mostprevalent in resistant populations cultured were Cooperia spp.On 45/61 (74%) farms where Cooperia spp were present in sufficient numbers, resistance to both ivermectin and albendazolewas evident. No cases of levamisole-resistant Cooperia spp weredetected. Resistance of Ostertagia spp to ivermectin was evidenton 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, andto levamisole on 4/46 (9%) farms. CONCLUSION: Anthelmintic resistance in parasitic nematodesof cattle is common in the North Island of New Zealand.Beef farmers need to be aware of the risks posed by anthelminticresistance, and routine FECR testing is recommended to ensureoptimal productivity and to guide decision-making when purchasinganthelmintics to be used on-farm.