Resistance

WORMER RESISTANCE

I've talked a bit about resistance to wormers because, just like with antibiotics, our wormers are becoming less effective. Worms are developing resistance to the chemicals we have available to treat them and growing numbers are no longer susceptible. This is extremely worrying because without effective treatment our horses are at risk of serious parasitic disease.

How does wormer resistance happen?

The more we use these drugs and expose the worms to the chemicals, the more quickly resistance develops. So, this is a very serious threat to our horses. But neither is it enough to simply widen the gap between treatments. At around 4-6 weeks from egg to adult, the lifecycle of the small redworm, is one of the quickest which means that a brewing parasite challenge can quickly get out of hand.

Instead, we need to be turning to targeted control, using worm egg counts every 8-12 weeks and other diagnostic tools wherever possible to reduce the frequency of chemical doses. This will go a long way to helping to prolong the life of our wormers.

Reference: Adapted from the American Association of Equine Practitioners (AAEP) and World Association for the Advancement of Veterinary Parasitology (WAAVP) internal parasite control guidelines, including research by Macdonald et al. (2023) and Nielsen et al. on anthelmintic resistance in cyathostomins (small redworms).
See:
https://aaep.org/guidelines/internal-parasite-control-guidelines
https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-023-05807-w

Image Source: Diagram courtesy of Westgate Labs. Used to illustrate the process of anthelmintic resistance in equine parasites.
https://www.westgatelabs.co.uk

Image from: www.westgatelabs.co.uk