Inefficacy of ivermectin against Cooperia spp. Infection in cattle

Authors: Pomroy WE, Bentall HP, Vermunt JJ, West DM
Publication: New Zealand Veterinary Journal, Volume 42, Issue 5, pp 192-193, Oct 1994
Publisher: Taylor and Francis

Animal type: Cattle, Livestock, Production animal, Ruminant
Subject Terms: Alimentary system/gastroenterology, Animal remedies/veterinary medicines, Anthelmintics, Parasite control, Parasites - internal, Nematode, Treatment/therapy
Article class: Correspondence

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Abstract: Ivermectin, either as an injectable or topical formulation, is used widely to control parasites in New Zealand cattle. These formulations have been well documented as having high efficacy against the major nematode species which infect cattle, although the efficacy against adult Cooperia oncophora is reported to be 95%. This is considered to be one of the doselimiting species. There have been two reports of lower than expected efficacy of the topical formulation against Cooperia spp. in cattle. In a slaughter trial, Bisset et al. found that ivermectin applied topically at the recommended dose rate of 500 μg/kg failed to achieve a statistically significant reduction in the burden of Cooperia spp. worms compared with untreated calves. The geometric mean of adult Cooperia spp. worms present in the treated calves was 5788 compared with 7524 present in the untreated calves. This reduced efficacy was not attributed to acquired anthelmintic resistance because ivermectin had not been used on the farm previously. In Australia, Eagleson and Allerton found in controlled field trials that ivermectin applied topically at 500 μg/kg ranged in efficiency in reducing faecal egg counts from 80.7% to 100%; four out of 13 trials achieving less than 90% and a further four were in the range of 90-95% reduction. Larvae obtained from the faeces of ivermectin-treated cattle on days 11-14 after treatment were predominantly Cooperia spp. We have further evidence from the field that ivermectin given either as an injectable or topical formulation may not be achieving a high degree of efficacy against Cooperia spp. in cattle…

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