Seasonal Parasite Control Winter

Winter parasite control ❄️ December - February

✅ Decide on your approach to encysted redworm; are you testing or treating?
✅ Have you tested for tapeworm in the last 6 months? EquiSal test if required.
✅ Are you in an area where you need to consider bots?
✅ If treating for redworm a reduction test is useful to monitor wormer efficacy.

There is one dangerous parasitic stage of the small redworm that we need to be particularly aware of at this time of year as it can have fatal consequences. Winter is the season to consider how we tackle the possibility of encysted redworm. This means either blood testing or treating with an appropriate wormer. 

If we need to treat then a moxidectin wormer is the preferred choice for most horses -  a 5 day fenbendazole is the other option which may be considered especially for youngsters or those who are very lean. We can also use this opportunity to reduction test to ensure our worming has been effective, particularly if using the latter chemical.


According to advice, horses with previous faecal egg count results of more than 200epg within the last year are considered high risk and may not be appropriate for this innovative new test, so should receive a routine treatment.

If your horse is classed as low risk with counts of less than 200epg over the last year, is in a closed herd with good paddock management and there is frequent poo picking, then chat to your vet further about this test. More information on the Small Redworm Blood test here.

Every horse that does not require a moxidectin dose is helping preserve to the chemical and delay resistance.

Step one: Please work out your horse's parasite risk level from the table below (click to view a larger version as a .pdf). If you need help assessing the risk then please email us for help. 

Step two: Using the table decide which route to take.

If your horse fits the low risk category you may choose to blood test with the vet for possible encysted redworm.
If medium or high risk category then dose with moxidectin for possible encysted redworm and bots.


If you aren't doing the blood test for encysted redworm we advise putting one (or in exceptional cases two) worming dose(s) into your annual parasite control programme. This is best done in the winter months between December and February. Ideally we aim to wait until the weather has turned before giving this dose. Small redworm activity slows considerably on pasture below 6 degrees Celsius so we are looking for the wintry weather and waiting for a few days where the daytime temperatures fall consecutively below this temperature. Worming after this time reduces the risk of reinfection and therefore many horses from needing a second treatment at the back end of the winter. 

This is why as our weather gets milder and more unpredictable our encysted redworm treatment has got later in the year. If we have a mild winter and the temperatures never dip, worm regardless before the end of winter.

You may have heard the advice to do your winter worming after the first frost - this will kill off any lingering bot flies and prevents any further bot eggs from being laid on the horse's coat where they may be ingested.

If you are subscribed to the All Seasons parasite control programme, then we will let you know when to treat based on your horses's tailor made programme and which season you have chosen to test for tapeworm.

> Any queries please get in touch



Equest Pramox, Equest, Panacur 5 day

Only two chemicals, moxidectin (in Equest and Equest Pramox) and five day courses of fenbendazole (Panacur Equine Guard) are licenced for the treatment of these encysted stages of small redworm. Moxidectin is the preferred treatment in most cases, particularly if you are also looking to target bots at the same time, because of widespread resistance to fenbendazole.

Equest contains only moxidectin while Equest Pramox has the addition of praziquantel meaning it also treats tapeworm. We would recommend testing for tapeworm first with the EquiSal tapeworm test and only giving the combination drug if you need to. More than 77% of horses won't need that extra chemical!

Warnings: Moxidectin shouldn't be given to underweight horses, foals under 4 months old (6.5 months if also combined with praziquantel) and isn't licenced for donkeys. We also advise caution if using it in miniature Shetlands unless you can calculate dosage accurately. This is because the active ingredient is stored in body fat and these animals don't have sufficient stores to take up the drug.

There are circumstances where a 5 day course of fenbendazole is more appropriate such as where moxidectin is contra-indicated.

If you are subscribed to the All Seasons parasite control programme, then we can advise you on what to treat with using the information within your horses's tailor made programme and also taking into account which season you have chosen to test for tapeworm.

> Any queries please get in touch


Just because you give a wormer it doesn’t mean it’s done the job we intended it to do. Resistance problems are rising across the five chemicals we have licenced to treat parasites in horses. Whichever drug you choose the winter dose is an ideal time to add in a reduction test to your programme. If your winter worm egg count is positive, treat with the appropriate product and do a follow-up worm count 10-14 days after worming to ensure efficacy of the drug.

Results from previous winter reduction testing revealed that 40% of horses wormed for encysted redworm with fenbendazole and 2.8% of horses wormed with moxidectin had parasites that were showing some resistance to the wormer. Tests also showed 50% of horses with a positive redworm count that had been treated with moxidectin had been under-dosed, leaving those horses more susceptible to developing resistant strains of redworm.

Vet Carolyn Cummins commented: “It’s imperative that we get worming right for the health of our horses. A simple treat and test can help to pinpoint potential problems and offer peace of mind that these important issues are under control. Resistance and the challenge to keep horses disease free from parasites is a very real problem and one that we should all be vigilant for.

“Speak to your vet or SQP about which wormer to choose for your horse, know your horse’s weight and dose accordingly this winter. A worm count two weeks later is a very cost effective way to check efficacy and that your worm control programme is working.”


More on Reduction testing

If you are subscribed to the All Seasons parasite control programme, then a reduction test is already included as part of your subscription. It will be sent out to you with your winter plan in accordance with your horse's individual programme.

Targeted Worming Programme



Wormers are very safe drugs and side effects are very rare. Some horses are however more sensitive than others. The very young, the very old and horses with immune systems compromised by conditions such as cushings, EMS and laminitis would be more at risk. If you are at all concerned then talk to your vet and consider these simple steps to minimise treatment risks:

  • Test first and only treat the worms you need to minimise dosing.
  • Avoid combination wormers; if you do need to give two chemicals separate out the different doses to give your horse's system less to deal with and administer them at least two weeks apart.
  • Use a high strength probiotic such as Protexin alongside worming.

Vet Liam Gamble MA VetMB MRCVS, from Protexin Equine Premium says: "Worming your horse can cause a sudden and marked effect on the gut ecosystem. The gut can become inflamed, motility is affected, and the microflora can become imbalanced. This is especially so when there are large numbers of worms or when the encysted larvae of the small redworm are targeted.

"Increased probiotic supplementation by using a product such as Protexin Quick Fix to give alongside worming will help to reduce the negative side-effects of the drug by promoting healthy gut bacteria."

> Shop Protexin Quick Fix