This year’s annual National Equine Health Survey, held in May, has revealed 20% of owners who claimed to have treated for encysted small redworm (ESRW) used a wormer that was not indicated to treat these potentially lethal encysted parasites.

Encysted small redworm,

As a result horses could be at serious risk, said worming experts at Zoetis, which recently introduced a campaign to help inform and educate about the dangers of ESRW.

ESRWs are one of the most common and harmful worms found in horses. They are the larval stages of the small redworm that have buried into the lining of the gut where they can lie dormant for some time.

They pose a potentially fatal health risk, but won’t show up in a standard faecal worm egg count. Untreated, ESRWs may develop and emerge en masse from the gut wall in early spring, causing diarrhoea and colic with a mortality rate of up to 50%.

“The veterinary recommendation is that all horses should receive a treatment for ESRW during the late autumn/winter, regardless of their faecal worm egg count,” said Wendy Talbot, national equine veterinary manager at Zoetis. “It’s crucial to remember that even if your horse’s faecal worm egg count is negative you must still treat for encysted small redworm before the early spring to protect your horse from this deadly parasite.”

Learn more about the Zoetis encysted small redworm awareness campaign at and test your knowledge before discussing the best treatment options with your vet or suitably qualified person (SQP).

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