The problem with pinworms and horses!


  • For many horse owners, we strive to balance their worming needs with what their environment tells us. Some of us follow a strict worming program, using a set schedule of rotating medications. Others of us do regular fecal egg counts, relying on test results to tell us when and what to medicate with.


  • On a side note here, remember that a fecal egg count tells us what worms have shed eggs….so a negative test may mean that your horse has worms, they are just not shedding eggs at the time of the test.


  • You must conduct regularly timed fecal egg counts, as different worms have different life cycles.


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So – what’s the deal with pinworms? Pinworms (AKA Oxyuris Equi) are worms that live in the last part of the large intestine.


  • At night, the female pinworm will leave the intestine through the anus and deposit eggs on to the sensitive skin around the anus.


  • This means your horse’s manure will not contain pinworm eggs!


This is a sign of pinworms! You will also need to rule out other reasons for tail rubbing.


  • This creates a very itchy situation….You may notice some tail rubbing and butt scratching going on! While this itching/scratching cycle can be caused by other stuff, you will need to determine if pinworms are the cause.


  • The pinworm eggs are deposited outside of your horse and are not passed in the manure. SO – what to do?


  • You and your veterinarian can test for pinworms by using regular old tape…. Your veterinarian uses tape to gently press against the anal region under your horse’s tail.


  • Microscopic examination of the tape will reveal (or not) the presence of pinworm eggs. You can then use the appropriate deworming medication to eradicate the problem.


  • You may also see a female pinworm protruding from your horse’s anus. I definitely suggest cleaning, inspecting, and observing all things under your horse’s tail. But would you have to camp overnight to see this?


  • Pinworms can also sometimes be seen on super fresh fecal balls. Or, if your horse has a rectal exam, the worms sometimes are carried out on your veterinarian’s covered arm.





You will also need to monitor other horses in the area, as the rubbing action of your horse will deposit the eggs into the environment where they can be picked up by other horses. It’s common in boarding situations for the entire barn to be dewormed at one time.


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**this will not test for pinworms – but gives your vet an overall view of your horse’s parasite load**

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