To De-Worm or not to De-Worm

There is a lot of conflicting information surrounding de-worming protocols for horses on the internet, making it difficult for owners to know what the best approach is for their horses. Included below are some commonly asked questions to hopefully help with all your de-worming woes!

  • Cyathostomes:


    Also known as small redworm or small strongyles, these parasites are of particular significance due to their prevalence and ability to ‘encyst’ into the gut wall where they can lay dormant for several years. Emergence of these parasites has the potential to cause severe consequences such as weight loss, colic, and anaemia. Adult redworms lay eggs which are detected in a faecal worm egg count. Encysted red worm burdens can be diagnosed via a simple blood test to check antibody levels. Importantly, horses can have high levels of encysted red worm but have a negative faecal worm egg count. This is due to the lack of active adult redworms laying eggs.




    Tapeworm eggs are intermittently shed from horses, meaning they can be missed on routine faecal worm egg counts. Tapeworms attach to the gut wall and live off food that horses ingest which can lead to weight loss, diarrhoea, and colic. Saliva testing has proven to be a simple and accurate test for diagnosing infections by measuring the antibody levels horses produce against tapeworm.




    Also known as ‘roundworms’, these large white worms tend to be more prevalent in foals and youngstock under four years old. Resistance often develops as horses age, making them less of a problem in adult horses, however they can become an issue in older, immunocompromised horses such as horses with PPID (Cushing’s disease). Foals can quickly accumulate large burdens of these worms which can lead to a noticeable inability to hold weight, severe debilitation, and unfortunately can be fatal. Due to the worm’s size, they can cause intestinal obstruction leading to colic, constipation, or diarrhoea, and larvae can also migrate into the airways causing coughing. Some other clinical signs of infection can include lethargy, a rough coat, and a pot belly appearance. Adult worms can be easily seen in faeces and eggs can be detected via a faecal worm egg count.




    Unlike the other parasites, pinworm isn’t a major threat to horse health, however infection can cause severe irritation around the rear end causing horses to rub themselves raw, leading to painful skin infections, and lethargy or depression. Yellow proteinaceous deposits can sometimes be seen around the anus or tail head region. Pinworms are diagnosed by an adhesive tape test performed around the anus and microscopic examination.

  • At MBM, we offer a worming programme which includes a tapeworm saliva test, 2 faecal worm egg counts, and a blood sample for encysted redworm. The cost for this programme includes all testing and wormers that are required for the whole year. If interested, please contact the office for information on how to enrol.


    Our recommended de-worming approach involves performing a tapeworm saliva test in January/February time, a faecal worm egg count in April/May, a faecal worm egg count August/ September, and an encysted redworm blood sample in November/December. These times are picked due to the life cycles of the worms that are being targeted.

  • Pregnant mares should have frequent faecal worm egg counts throughout the duration of their pregnancy and should receive a suitable wormer within the last month of pregnancy. This is to decrease the risk of worms being passed from the mare to foal. Please contact us to discuss further which products are suitable for your pregnant mare as this will vary depending on their previous worming and yard worming history.


    Foals should not be wormed until 6 weeks of age. We recommend worming foals at 6 weeks old and repeating every 6 weeks with a one-off fenbendazole wormer (Panacur) until they are 6 months old. At 6 months old, they can begin routine testing similar to adult horses, however, faecal worm egg counts should be performed more frequently due to the increased risk for higher worm levels. More frequent testing should be continued until the horse is 4 years old.

  • Due to ‘blanket’ de-worming approaches, there has been evidence of resistance to some commonly used wormers. At this time, there are currently no further wormers being developed, so it is imperative that we limit usage of wormers to only those horses that are in need of them. This has led to the recommended testing approaches listed above, ensuring only those that require wormers receive them, limiting further resistance developing. We commonly will ask for another faecal sample 2 weeks after your horse has been de-wormed to ensure that their faecal worm egg count is decreasing, meaning that they are not resistant to the wormer they were prescribed.

  • The table below includes the common wormers available on the market and what worms they target. At MBM, we do not recommend repetitive usage of Equest or Equest Pramox as this wormer is considered to be quite strong and can persist in the tissues for a long time. Please do not hesitate to contact the practice for further guidance on which wormer would be best suited for your horse(s).

Wormer Drug Ascarids Adult Redworm Encysted Redworm Tapeworms Pinworm Pregnancy safe? Comments
Panacur- One off Fenbendazole Yes Yes     Yes Yes  

Panacur Guard - 5-day course

Fenbendazole Yes Yes Yes   Yes Yes  
Strongid P, Pyratape P Pyrantel embonate Yes Yes   Yes* Yes Yes *Double dose required to target tapeworm
Bimectin, Animec, Eqvalan Ivermectin Yes Yes     Yes    
Equimax Ivermectin & Praziquntel Yes Yes   Yes Yes Yes  
Equest Moxidectin Yes Yes Yes   Yes   Care with those prone to colic; not for foals < 6 months
Equest Pramox Moxidectin & Praziquantel Yes Yes Yes Yes Yes   Care with those prone to colic; not for foals <6 month
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