A British survey has revealed that half of all horses and ponies are not being dewormed correctly for encysted small redworm, the most common worm found in equines.
Worming experts at Pfizer Animal Health are alarmed about the results of the survey, which was conducted as a part of the National Equine Health Survey (NEHS) in May 2012. They said encysted small redworm – one of the life stages of small redworm – may account for up to 90% of the redworm burden in the horse1 and can pose a very serious health risk.
The small redworm is the most common worm found in horses today.
Pfizer said it was important that horses are treated properly during late autumn or winter. “However, the new data has alarmingly revealed that this isn’t happening in around half of all cases.”
The survey showed that only 50% of 1095 respondents wormed their horse with an effective product for the control of encysted small redworm. The remainder either used a product they incorrectly thought treated encysted small redworm or simply didn’t worm their horse or pony at all to control the parasite. The most common reason given for not treating for encysted small redworm was that the horse had had a clear fecal worm egg count.
Wendy Talbot, Pfizer’s vet advisor, explains why this is so concerning: “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 redworms2, which can present a potentially fatal health risk to the horse.”
Encysted small redworms can remain dormant inside a horse for up to two 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.
Pfizer said it was imperative to use a wormer containing moxidectin or fenbendazole 5 day course, licensed to treat encysted small redworm. It is important to remember that there is now widespread resistance to fenbendzole in parasite populations4, whereas moxidectin has been shown to be effective against benzimidazole resistant worms and has a 13 week recommended dosing interval.
Mary King, Olympic three day eventing team silver medallist, routinely treats all her horses for encysted small redworm in the early winter each year.
She says: “Treating small redworm is a big priority on my yard to help make sure the horses stay in peak health. We tend to use Equest, after the first frost of the season. This way we can also tackle bots effectively with the same dose.”
• Pfizer has created Stable Mate, a new App that makes it easy to manage daily equine healthcare, including worming. Stable Mate is free from the iPhone App Store.
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