06/02/2026
🪱 Encysted Small Redworm 🪱
What are encysted small redworm?
Small redworm have an unusual stage in their life cycle where the larvae burrow into the wall of the large intestine and become encysted. They can remain hidden in the gut wall for months or even years, often building up in large numbers.
While encysted, they can interfere with nutrient absorption, sometimes leading to weight loss and poor condition. The greatest concern is when a change in conditions such as a seasonal change triggers a mass emergence of larvae, which can result in acute and potentially serious disease.
What has traditionally been done?
At this time of year, it has been common practice to worm all horses with moxidectin, often after a period of hard frost, to target encysted stages of redworm.
So how do we know if your horse actually needs a wormer?
Using a targeted, evidence-based approach allows us to tailor treatment to your horse’s individual risk. You can find out your horses risk at www.whatsyourwormrisk.com
🐎 Lower-risk horses
Horses with consistently low faecal egg count (FEC) results throughout the year are less likely to carry a high worm burden and often don’t require routine treatment for encysted redworm.
In these cases, a small redworm blood test can help us decide whether treatment is needed by detecting antibodies to redworm.
🐎 Higher-risk horses
Higher-risk horses are more likely to carry a significant worm burden and to develop worm-related disease. For these horses, we would recommend treatment for encysted redworm using a moxidectin-based wormer (e.g. green Equest).
More about the small redworm blood test
🩸 This is an antibody test that helps determine the presence or absence of a total redworm burden
🩸 It reflects exposure to all stages of redworm and is not specific to encysted larvae
🩸 A positive result does not automatically mean treatment is required
🩸 Results must be interpreted alongside worm egg counts and your horse’s clinical history
⚠️ This test is not appropriate for medium- or high-risk horses, where treatment is usually the recommended approach
📅 The ideal testing window is September–December, but this can be extended to April if missed
⚠️ Testing should not be performed within 4 months of the last moxidectin treatment
Already wormed this winter?
No problem, just keep this information in mind for next year. Developing a targeted worming plan based on your horse’s individual risk, supported by worm egg counts and testing, helps reduce unnecessary wormer use while still protecting your horse’s health.
If you have any questions or would like advice on testing or parasite control, please feel free to contact the practice.
