The fecal egg count test for your horse, and when you should do it!


This test measures the presence of small strongyles and ascarids, also known as roundworms. They are both totally gross. More on that later.


The fecal egg count test (FEC) is designed to detect specific types of parasites that your horse is carrying around. This test won’t catch everything, as some worms, like the pinworm, don’t release eggs inside your horse, so they will usually never show up in manure. The fecal egg count test as done for horses measures the load of small strongyles and ascarids.


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What the heck are small strongyles and ascarids?

Small strongyles are nasty parasites that your horse can house in his intestine.


  • They are picked up when your horse is grazing. In the pasture, small strongyle eggs that are left by a horse’s manure turn to larvae. Your horse will eat these larvae, and the larvae migrate to the large intestine and the cecum. There, the small strongyles will burrow into the intestinal wall and form their own cysts – sort of like a worm nest. Sometimes they live there for months, sometimes years.


  • When all of the stars align, these encysted larvae burst out and start to transform into their final larval stage in your horse’s gut. They will start to lay eggs, to be passed with your horse’s manure back into the pasture.


  • The main problem with small strongyles is that dewormers are unlikely to be able to penetrate the cyst to kill the larvae. Also, if the larvae all break out at once, which can happen, your horse can develop dangerous colitis, diarrhea, or colic. You know, big Vet bill stuff.


Ascarids, or roundworms, are also quite cringe-worthy.


  • These roundworms are usually only found in foals and young horses, but turns out, adult horses can also harbor them. Here’s where it gets gross – some ascarids can be over a FOOT LONG. Like 15 inches long. And in plentiful numbers, will steal nutrition and blood from your horse. Not to mention creating a literal blockade in his gut.


  • If you thought that was gross, hang on. The life cycle of the ascarid is barf-tastic. Your horse will eat some ascarid eggs in the pasture. They hit the small intestine hatch into larvae. The ascarid larvae will then burrow through your horse’s body – from the intestine to veins to liver to heart and to the lungs. When in the lungs, your horse will cough up the larvae and then swallow them. Back in the intestines, they mature to lay eggs of their own and start the cycle again.


horse worms in a jar

Ascarid in a jar. Where it belongs.


What does this have to do with my horse’s fecal egg count?


  • When you have a fecal egg count test done on your horse, a small sample of manure is sent to a lab for analysis. The results will indicate a number, such as 100 or even 300 or more, even up to 1000. The unit of measure is the eggs per gram, the EPG. This tells us how many strongyles and ascarid eggs are passing per gram of manure.


  • If your horse comes back with an EPG of 200, and your friend’s horse comes back with an EPG of 400, this does not mean your friend’s horse has twice as many parasites. It simply means that some horse shed eggs differently – and this number can be influenced by the horse’s health, immune system, when he was last given a dewormer, the time of year, and even how old the parasites in his body are.


  • The EPG number tells your Veterinarian if your horse is a low, medium, or high shedder. Generally speaking, low shedders and some medium shedders do not need deworming. Work closely with your Veterinarian about your horse, his FEC results, and how to proceed with deworming – or not.


When should you perform the FEC test?


  • There are two things to consider about timing the fecal egg count. Will you be performing the fecal egg count reduction test, and what season is it? This measures the effectiveness of your dewormer, and can let you know if your horse needs another brand, if possible. This is also an indication of the parasite’s resistance to modern dewormers.


  • One easy way to do the FEC test is to use a service, like These handy mail-in kits are affordable and accurate. Doing your own equine parasite testing allows you and your Vet to diagnose the extent your horse’s internal parasitic infection or burden is BEFORE you deworm. That way, you know which parasites you are treating for.


  • When you do a follow-up test, you can tell if your dewormer is working. This is the fecal egg count reduction test, or FECRT, protocol. The follow-up or post-treatment test results are important because it also lets you know if your horse’s parasites have developed any resistance to the dewormer you are using to treat them.


  • After the initial fecal egg count, deworm according to your Veterinarian’s plan, and perform another FEC test two weeks later to measure the effectiveness of your dewormer. This reduction test does not prove conclusively that parasites are resistant to that dewormer, it’s only a gauge and a place to start. Regular fecal tests and accurate deworming with follow-up tests over time starts to show trends.


picking up manure in a pasture

Pick a fresh sample for your horse’s fecal egg test.


Also, allow for the FEC to be done at the right stage of the parasite’s life cycle. Your vet can help you determine the best time according to your climate and location, among other factors.



  • From – “Chemical dewormers can only control parasites when they are inside your horse. Therefore another factor in considering when the best time is to treat your horse for parasites is the actual life cycle of the parasite.


  • Most parasites start as an egg. The egg matures into a larva and the larva matures into an adult. The adult lays eggs and the cycle starts all over again. Internal parasite eggs are expelled in your horse’s manure and need a little time to mature outside your horse prior to becoming infectious and being consumed by your horse he grazes in a pasture.”


What time of year should you run the FEC?


  • Parasites reproduce and are most plentiful when the weather warms-up but before it gets too hot, which means Spring and early Summer. Since that’s when “parasite season” begins, Spring and early summer are also one of the best times to test. Performing an Early Spring fecal egg count test on your horse allows you to set a parasite burden baseline for treatment and future testing comparisons.


  • Parasites tend to slow or stop reproduction as the weather turns colder. Therefore, a Fall fecal egg count test result will provide you with your horse’s parasite burden going into winter and allow you to deworm accordingly for the remainder of the year.


fecal egg count test to mail in

Three steps to collecting your horse’s manure and submitting your fecal egg count – fill out paper, collect fecal ball, mail.


How hard is the fecal egg count test to run?

  • It’s quite easy, however, without gloves you might find it more difficult! Test kits require a collection of a fecal ball. You will need to mail it a super fresh sample with a coolant in the box so it doesn’t cook along the way.


  • All supplies you need are included in the Zero Egg Count kits along with directions. Which you should read. This isn’t DIY furniture that inevitably leaves you with random screws and such left over, it’s your horse’s health! You want the fresh sample to arrive uncooked and unfrozen after following the simple instructions.


How often are you doing fecal egg tests?

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