06/01/2025
*** ENCYSTED REDWORM ***
I first posted this in 2019, but after reading a LOT of worrying comments recently about how people don’t worm their horses at all, as they do worm egg counts, I thought it was time to do a little encysted redworm refresher, with some updates!
1. Redworm can kill your horse.
2. You need to worm for encysted redworm AFTER they encyst, and before they emerge, so NOT in the Autumn! Wait for a good, frosty cold spell.
3. Encysted small redworm are NOT DETECTABLE in worm egg counts.
4. The larvae of small redworm, “encyst” or burrow into the gut wall. These can cause fatal consequences when they re-emerge.
5. Redworm appear as tiny pieces of thread in your horse’s droppings. They are very short and thin, and can be hard to see. They are white if they haven’t yet fed, and red if they have fed.
6. A horse can appear completely normal and healthy whilst carrying a large redworm burden. However, weight loss and diarrhoea may be early indicators; don’t ignore these signs.
7. Most wormers DO NOT target encysted redworm. Only TWO do: Fenbendazole and Moxidectin.
8. Lots of combination wormers contain IVERMectin. This WILL NOT have any effect on encysted redworm. The only wormer that contains MOXIDectin, is EQUEST. The Pramox (blue) version will treat tapeworm at the same time. Don’t use Pramox if you have treated separately for tapeworm, or used a saliva or blood test for tapeworm. Use the normal Equest (green) if this is the case.
9. Redworm are eaten by the horse during grazing. The larvae start to burrow into the gut wall as temperatures drop. Treating for encysted redworm whilst temperatures are warm, is not the optimal time, as the larvae may well not have started to encyst. Treating after a few hard frosts, also reduces the level of reinfection from larvae already on the fields.
10. The larvae stay in the gut wall during the winter, and are then triggered to emerge from the gut wall as the temperatures warm up in the Spring. If the horse has not been treated for redworm during this redworm “hibernation” stage, he/she is at risk of developing CYATHOSTOMINOSIS.
11. Cyathostominosis has a mortality (death) rate of up to 50%. It presents as colitis; profuse diarrhoea and colic. Contact your vet immediately if you see these symptoms in your horse at any time of year, but it is more likely to be due to redworm if this occurs in the Spring.
12. Ensure you have treated for encysted
redworm before temperatures start to increase as Spring arrives, incase of a large encysted redworm burden that may suddenly emerge.
13. There is a blood test for all stages of redworm, including encysted. This detects antibodies, so may be positive if your horse has had a high burden in the past 6 months, even if he currently doesn’t, but worth discussing with your vet. I would not be recommending this route for high risk redworm horses ie horses in herds with no poo picking, or rescue cases.
14. 5 day Panacur Guard (Fenbendazole) is the only other wormer that can treat the encysted stage of redworm. There was widespread resistance to this wormer, and a huge move towards everyone using Moxidectin for encysted redworm. It is my wormer of choice for very sick or poor horses, due to its milder action over 5 days. However, there is some evidence that it may cause more damage to the gut than Moxidectin, so more research is definitely required!
15. Poo picking daily is perfect pasture management, but does not mean that your horse is worm free! You still need to egg count/blood test for all worms and/or worm.
16. Herbal wormers do not work.
17. Worm egg counts do not detect encysted redworms (or tapeworm/bots/pinworm). I realise I am repeating myself, but this is something that lots of people still do not realise.
18. Do not UNDERDOSE when worming, as this will aid resistance. If in doubt, add 50kg to the weigh tape weight of your horse. Wormers are very safe with regards to toxic doses.
19. The Mole Valley wormers are NOT the same as Equest!!!! I saw this misinformation posted yesterday! They contain Ivermectin, which will NOT treat for encysted redworm.
20. Do NOT overuse Equest. Moxidectin (Equest and Pramox) should only be used ONCE in a 12 month period. So know when to use it!
This is not an exhaustive review of redworm, and I may add to the list if I think of anything else, but I hope this is of some use! Worming regimes and what worm egg counts detect, seems to cause lots of confusion amongst horse owners, and even yard owners.
Blood tests currently used for tapeworm and redworm, measure antibody levels to the worm. The saliva test also measures antibodies. The concern here would be false positives. This means the test coming back as positive when your horse has been clear of the worm in question for months. Antibody levels remain high for months following successful treatment for the worm being tested for. However, a negative obviously means the horse has been clear for a good few months, and would not need worming.
Happy reading!
Please share, as this is really something that all horse owners should know, and still don’t!
No prizes for spotting the hundreds of redworm in this photo!
