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Wednesday, 12 December 2012

Worming horses to treat for encysted small redworm

Worming experts at Pfizer Animal Health are alarmed about the results of the National Equine Health Survey (NEHS) May 2012 survey
A recent survey of horse owners has shown that nearly half are not worming their horses correctly when it comes to treating encysted small redworm. Encysted small redworm (small strongles/cyathostomes) are the most common worms found in horses today and may account up to 90% of the redworm burden in the horse 1. The recent survey has revealed that treatment for encysted small redworm is only been done by about half of the survey respondents.
The survey which was conducted in May 2012 as part of the National Equine Health Survey (NEHS) showed that out of 1095 respondents only 505 had wormed their horse with an effective product for the control of encysted small redworm. The remainder had either used a product that they thought treated encysted small redworm when in fact it did not or they simply did not worm their horse or pony at all. The most common reason for not treating for encysted small redworm was that the horse had had a clear faecal egg count.
“Encysted small redworm won’t show up in a standard faecal worm egg count – even if the horse has shown a negative or low count it could still be harbouring several million encysted small redworms 2, which can present a potentially fatal health risk to the horse” says Wendy Talbot Pfizer’s vet advisor.

Encysted small redworm can remain dormant inside a horse for up to 2 years, but usually develop and emerge from the gut wall all at the same time in the early spring. In severe infestations mass emergence can lead to a disease syndrome known as “Larval cyathostominosis” causing diarrhoea and colic with up to a 50% mortality rate3.
It is most important to use a wormer containing moxidectin or a 5 day fenbendazole course licensed to treat encysted small redworm. It is important to remember that there is now widespread resistance to fenbendazole in parasite populations4whereas moxidectin has been shown to be effective against benzimidazole resistant worms and has a 13 week recommended dosing interval
1          Bairden K. et al (2001) Veterinary Record 148, 138-141
2          Dowdall S. et al (2002) Veterinary Parasitology 106, 225-242
3          McWilliam H. et al (2010) International Journal for Parasitology 40, 265-275
4          Matthews JB (2008) An update on cyathostomins: Anthelmintic resistance and worm control. Equine Vet. Education 20 552-560