Worming experts at Zoetis are warning that the risk of larval cyathostominosis may be higher than usual this year, following the UK’s exceptionally mild, wet winter.

Encysted small redworm

Early spring is the high-risk time for  the disease, which is a potentially fatal syndrome caused by the mass emergence of small redworm from their dormant, encysted state.

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 rate.
Lower environmental temperatures during the winter months usually prevent worm eggs and larvae from developing on the pasture, meaning that reinfection of horses does not occur to a significant extent until the following spring. However, unusually mild, wet winters – such as this year’s – mean worm eggs and larvae can develop on the pasture and grazing horses can become reinfected.

Even horses that have been treated for ESRW in late autumn/early winter may still be at risk of re-infection, particularly if they have been turned out on heavily used pasture.

Zoetis veterinary surgeon Wendy Talbot said: “It is recommended that all horses receive a treatment for ESRW during the late autumn/winter, regardless of their faecal worm egg count. 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. 

  • To find out more about year-round worm control, visit www.wormingyourhorse.info.
  • Visit www.esrw.co.uk to test your knowledge of encysted small redworm.
  • Stable Mate, the horse health management App from Zoetis, is available for iPhone and Android.
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