Mild winter may increase small redworm risks warns Zoetis

London, UK, 26 March 2014 – Early spring is the high-risk time for larval cyathostominosis, a potentially fatal syndrome caused by the mass emergence of small redworm from their dormant, encysted state. Worming experts at Zoetis are warning that this year, the risk of disease may be higher than usual, following the UK’s exceptionally mild, wet winter.

Encysted small redworm (ESRW) are one of the most harmful parasites to affect horses in the UK. They are larval stages of the small redworm that hibernate in the lining of the gut and don’t show up in a standard faecal worm egg count. They usually ‘wake up’ in the early spring and their mass emergence can lead to larval cyathostominosis, causing diarrhoea and colic with up to a 50% mortality rate1.

Normally, during winter months, lower environmental temperatures prevent worm eggs and larvae from developing on the pasture, meaning that re-infection of horses does not occur to a significant extent until the following spring. However, during unusually mild, wet winters such as this year’s, worm eggs and larvae can develop on the pasture and grazing horses can become re-infected2. Even horses that have been treated for encysted small redworm in late autumn/early winter may still be at risk of re-infection, particularly if they have been turned out on heavily used pasture.

“It is recommended that all horses receive a treatment for ESRW during the late autumn/winter, regardless of their faecal worm egg count3,” said Wendy Talbot, Zoetis veterinary surgeon. “In some circumstances, such as if the preceding winter has been especially mild, then it is advisable to consider a second ESRW dose in the spring for those horses most at risk.”

All horses can develop larval cyathostominosis but those at particular risk are youngsters, old or immune-compromised horses (such as those with Cushing’s disease), those with an unknown or sub-optimal worming history and those that were not dosed correctly in late autumn/early winter. If you have a horse showing signs possibly related to a worm burden such as loss of condition, sudden weight loss or diarrhoea, it’s important to contact your veterinary surgeon as soon as possible.

To find out more about year-round worm control, visit You can also visit to test your knowledge of encysted small redworm. Stable Mate, the horse health management App from Zoetis, is available from the iPhone App Store and Google Play Store: text Stable Mate to 80800 to download.

  1. Dowdall S.M.J. et al (2002) Veterinary Parasitology 106, 225-242 
  2. Reinmeyer CR and Nielsen MK (2013) Handbook of Equine Parasite Control. 45-53
  3. Nielsen (2012) Veterinary Paristology. 185. 32-44

About Zoetis 

Zoetis (zō-EH-tis) is the leading animal health company, dedicated to supporting its customers and their businesses. Building on more than 60 years of experience in animal health, Zoetis discovers, develops, manufactures and markets veterinary vaccines and medicines, complemented by diagnostic products and genetic tests and supported by a range of services. In 2013, the company generated annual revenues of $4.6 billion. With approximately 9,800 employees worldwide at the beginning of 2014, Zoetis has a local presence in approximately 70 countries, including 28 manufacturing facilities in 11 countries. Its products serve veterinarians, livestock producers and people who raise and care for farm and companion animals in 120 countries.  For more information, visit

Author: News Editor

Share This Post On
468 ad