The hidden parasite threat of encysted small redworm during winter
Late Autumn/Winter is a key moment in the equine year as we need to consider the hidden parasite threat of encysted small redworm. The encysted larval stages of redworm burrow into the gut wall and lie dormant, often for months at a time. Crucially, these larvae do not produce eggs, which means they cannot be detected through a routine faecal worm egg count.
This is why winter parasite management looks a little different to other seasons. Horse owners should start by understanding their horse’s individual parasite risk profile and whether they're low, medium or high risk for disease caused by worm burdens. Horse owners can then use Westgate's Winter Protocol Flow Chart to help guide them through the decision making process and identify the most appropriate way to manage encysted redworm for every horse in their care.
Low risk horses are those with a proven history of consistently low faecal egg counts, defined as under 200 eggs per gram for at least a year. These horses typically live in a closed herd, benefit from good paddock hygiene with frequent poo picking, and have not received a worming treatment within the last four months. Horses meeting these criteria may be suitable candidates for the small redworm blood test, arranged through your vet. This test can help assess whether treatment for encysted larvae is necessary, avoiding unnecessary use of wormers.
For horses considered at higher risk, the blood test is not appropriate and treatment for encysted redworm is advised. Currently, only two drug options are licensed for targeting the encysted stages of small redworm, moxidectin and a five-day course of fenbendazole. Choosing the correct product is not always straightforward, so advice from a vet or SQP is essential to ensure the most suitable and responsible choice for each individual horse.
ASSESS YOUR HORSE'S PARASITE RISK PROFILE
With resistance continuing to rise across the five chemical groups licensed for use in horses, winter also presents an ideal opportunity to build chemical monitoring into a worm control plan. If a winter worm egg count is positive, treatment should be followed by a worm count reduction test carried out 10 to 14 days later. This simple step confirms whether the chosen chemical has worked effectively and helps protect the usefulness of wormers for the future.
Taking a thoughtful, evidence led approach during the winter months supports not only the health of individual horses, but also the long term sustainability of parasite control across the wider equine population. If you haven't yet taken steps to address the possibility of encysted small redworm in your horse then it's recommended to do so now before Spring, when we can once again resume regular worm egg counts through the season.
