Concerns about incorrect of wormers for sheep scab

The incorrect use of injectable wormers to control sheep scab in NI is highlighted as a “particular concern” in a new research paper.

Published in the scientific journal Vet Record, the paper draws on findings from a pilot project which investigated sheep scab outbreaks in 60 flocks across NI.

Vets and scientists from the NI Sheep Scab Group found that injectable wormers in the macrocyclic lactones (ML) group, such as Dectomax and Ivomec, were commonly used for scab treatment.

The researchers state that whilst ML products can be an effective treatment for individual animals, it has “insufficient persistence” so scab mites can continue to linger in a flock.

The paper states that the “greatest concern” is that overusing ML wormers gives the opportunity for resistance in both intestinal parasites and the sheep scab mite to develop.

“Some farmers reported that prior to their involvement in the project, they had to use a second, or in one case a third ML treatment, often ultimately dipping the flock, before they considered scab to be eradicated,” the paper reads.

The project found that there were no reports of treatment failure when flocks that had a scab outbreak plunge dipped sheep with an organophosphate dip product.

By comparison, six farmers in the project that used an injectable ML wormer to treat sheep scab agreed to be re-tested, with four of them returning a positive test result.

“Prescribers should be urged to consult, in detail, about the clinical needs, expectations and requirements of farmers seeking a preventative scab treatment, particularly when asking for an ML,” the paper reads.