• 22 January 2015

Survey shows 20% of Owners Unaware of Encysted Small Redworm Risk

This year’s annual National Equine Health Survey*, held in May, has revealed that one in five 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.

This may leave horses at serious risk, said the worming experts at Zoetis, who recently introduced a campaign to help inform and educate about the dangers of ESRW.

Encysted small redworms 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, encysted small redworm may develop and emerge en masse from the gut wall in the early spring, causing diarrhoea and colic with a mortality rate of up to 50%1.

“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,2,3” 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.”


1. Dowdall S.M.J. et al (2002) Veterinary Parasitology 106, 225-242

2. Nielsen (2012) Veterinary Paristology. 185. 32-44

3. AAEP (2013) Parasite Control Guidelines

* The National Equine Health Survey, conducted by the Blue Cross and supported by Zoetis, was completed by 3,669 horse owners in May 2014. The survey contained 25 questions on general horse health, care and management and was validated by Professor Josh Slater of the Royal Veterinary College.


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