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If you haven’t yet treated your horse for encysted small redworm this winter you should do so as soon as possible, to help prevent potentially fatal disease, advises Zoetis.
Encysted small redworm (ESRW) are the larval stages of the small redworm. They hibernate in the lining of the horse’s gut where they won’t show up in a faecal worm egg count. They usually emerge in the early spring and may cause a condition known as larval cyathostominosis, resulting in diarrhoea and colic, with a high death rate.
Every horse should receive an annual treatment to combat encysted small redworm, ideally during November/December and certainly before the spring arrives. It’s imperative that the correct wormer is used, but worryingly one in three horse owners are still struggling to get it right. Last year’s National Equine Health Survey showed that only that 64% of those who specified how they treated for encysted small redworm had correctly used a wormer containing moxidectin and 7% had used fenbendazole. However, of the remainder, 22.5% had incorrectly used a wormer containing ivermectin, which does not treat for encysted stages and 6.3% had used products licensed for tapeworm treatment only.
There are only two active ingredients licensed to treat for encysted small redworm: a single dose of moxidectin or a five-day course of fenbendazole. Resistance to fenbendazole is now widespread in the UK so a resistance test is recommended before using it.
Given the prolonged mild conditions this winter it is advisable to carefully discuss your worming plan with your prescriber to make sure it continues to be suitable for your horse. Small redworm eggs and larvae can survive on the pasture for longer when it’s warmer, increasing the window of opportunity for grazing horses to become infected.
Wendy Talbot, veterinary surgeon at Zoetis, said: “Don’t assume that because your horse looks well there isn’t a problem. Encysted small redworm won’t show up in a faecal worm egg count. They may not cause any obvious symptoms either so you may not know your horse has got them.
“Always discuss your worm control plan with your vet or suitably qualified person (SQP) and use the right product at the right time to safeguard your horse’s health. Remember to assess weight using a weigh tape or weigh bridge to avoid under-dosing and to prevent building resistance.”