Winter Worming Action Plan

December 29, 2018


Winter can be a particularly busy time for horse owners. Battling rain, cold, and mud, extra mucking out and short, dark days, alongside the usual influx of festivities and social events can soon add up and leave you seriously lacking in time and energy. Potentially falling by the wayside during these months is your horses’ worming schedule. Do you even need to worm in winter? What for, what with, and when?


Read on to find out how to make your winter worming straight forward but effective!


Encysted Redworms

During the winter months it is crucial that horses are treated for encysted redworm, regardless of the programme followed during rest of the year. At this time, many species of Small Redworm (Cyathostomes) larvae, which are already in your horses’ system, burrow themselves into the wall of the large intestine.


Although some continue to develop and emerge after a short period as mature, egg laying worms, many lay dormant in this stage for up to three years. Tens of thousands of individuals can line the intestine wall, impairing the horse’s ability for nutrient absorption, often resulting in weight loss and potentially life-threatening illness.


An increase in daylight hours and temperature during the change from Winter to Spring can trigger a ‘mass emergence’ of these encysted worms. This emergence can cause colitis or larval Cyathostominosis (bowel inflammation), which can be life threatening for the horse, and requires immediate veterinary attention.

What can be done?


It is now normally advised that wormers should be administered after investigative Egg Counts have been carried out, this is not the case with treatments for Encysted Redworms, as they are not laying eggs, therefore there is not a test for them (yet). 


Therefore, during the winter months one of the two drugs licenced to target Encysted Redworm should be administered. These two chemicals are Moxidectin, found in the Equest wormers (Equest and Equest Pramox) and Fenbendazole, present in the 5-day course of Panacur Equine Guard.


It is important to carefully choose the correct drug for your horse. For example, Equest contains only Moxidectin, whereas Equest Pramox combines both Moxidectin and praziquantel, and so treats Tapeworm as well. It is recommended that Equest Pramox is only administered at this time if your horse hasn’t been treated for Tapeworm in the last 6 months and has a negative result from an Equisal Tapeworm test, so as to not contribute to the risk of resistance developing amongst the Tapeworms to the Praziquantel wormer. 77% of horses will not require the addition of Praziquantel in their winter worming dose.


* Moxidectin shouldn't be given to underweight horses, foals under 4 months old (6.5 months if also combined with praziquantel i.e Equest Pramox) and isn't licenced for donkeys*



Peace of Mind

As with all wormer treatments, it is important to check that the wormer has worked, and that the worms haven’t developed a resistance to them, via a resistance test, 10-14 days after the drug is administered. It is particularly important to check for resistance at this time of year, as the drugs used are often avoided throughout the year, and set aside for treatment of Encysted Redworm, and therefore their efficacy is infrequently checked.


Throughout the winter months (December – February, inclusive) resistance tests with Target Worm Counts are just £5.


For more information, including a tailor-made worming schedule, or to arrange your resistance tests please get in touch:





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