Confirmation of ivermectin resistance in Ostertagia ostertagi in cattle in New Zealand

摘要: Abstract Six suspected cases of ivermectin resistance in Ostertagia spp. cattle were investigated after routine anthelmintic efficacy testing on commercial farms. On four farms a comprehensive faecal egg count reduction test (FECRT) was undertaken using oral formulations (0.2 mg/kg), albendazole (10 mg/kg) and levamisole (7.5 mg/kg) while two only tested. The proportions the untreated control post-treatment larval cultures used to apportion counts genera determine against this genus. Isolates recovered from three each infect 18 six month old calves. moxidectin, both at 0.2 mg/kg, determined isolate by slaughter worm count. , based differentiated FECRT for varied 0% 88%. trial 13% 75% but moxidectin was >99% effective all isolates. In addition, albendazole, dose rate 10 mg/kg, failed achieve 95% (82% 85%). Levamisole consistently which is consistent with its known lesser parasite. These results confirm presence macrocyclic lactone resistant O. ostertagi New Zealand likely dual resistance, lactones some Resistant populations highly pathogenic parasite are probably not uncommon pose significant threat animal production welfare future.