Confirmation of resistance to ivermectin by Cooperia curticei in sheep

Authors: Hughes PL, McKenna PB
Publication: New Zealand Veterinary Journal, Volume 53, Issue 5, pp 344-346, Oct 2005
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Alimentary system/gastroenterology, Animal remedies/veterinary medicines, Anthelmintics, Parasite control, Parasites - internal, Nematode, Diagnostic procedures, Slaughter, Treatment/therapy, Research/development
Article class: Short Communication

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Abstract: AIM: To investigate the occurrence of resistance to a full dose of oral ivermectin by Cooperia curticei in sheep.
METHODS: Twelve lambs on a sheep and cattle property in the North Island of New Zealand were randomly allocated to one of two equal-sized groups. One group was treated orally with a single dose of ivermectin at the manufacturer’s recommended dose rate of 0.2 mg/kg, while the other remained as an untreated control. Worm counts were carried out post mortem on the abomasa and small intestines of all animals in both groups 7 days after treatment.
RESULTS: While treatment with ivermectin reduced the numbers of all other worm genera to almost zero, those of Ostertagia(= Telodorsagia) circumcincta and C. curticei were reduced by only 37% and 19%, respectively.
CONCLUSIONS: These results provide clear evidence of resistance to ivermectin by O. circumcincta and C. curticei. They also appear to represent the first record of macrocylic lactone (ML) resistance in C. curticei in sheep in New Zealand or elsewhere.
KEY WORDS: Ivermectin, Ostertagia, Cooperia, sheep, anthelmintic resistance, controlled slaughter trial

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