How to reduce your horse’s parasite load!



What does “parasite load” mean?


It’s basically how many worms and other parasites, like strongyles and bots, that your horse carries around with them. Fairly logical, right? But it’s really hard to measure this as the life cycles of horse parasites vary. The best way we have is to measure their parasite load by the number of eggs that your horse is passing. We do this with a fecal egg count (FEC) test.


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What factors contribute to a horse’s parasite load?


  • This is partly the individual horse and partly environment and partly barn and pasture management. For young horses, you might notice them getting a bit of a round belly. It’s not from beer.


horse worms in a jar

So many “BLECHS” shares this information:

“However, every horse’s situation is different, even those within the same barn or the same pasture. Following are some factors that can affect your horse’s worm load:


  • Age – foals and young horses are more susceptible to certain parasites


  • Location – certain parasites are more common in some geographical areas or climates


  • Season – some parasites are only active during particular seasons


  • Travel – potentially exposes your horse to other parasite infected horses


  • Pasture Load- horses continually grazing in a given area may increase parasite exposure


  • Pasture Mates – other animals can carry parasites that may infect your horse


  • Stress – may compromise a horse’s immune system


  • Health – horses with infections or certain metabolic diseases may be more susceptible to parasites”


Why does parasite load matter? It matters because parasites can lead to all sorts of problems.


  • Internal parasites do a few things inside your horse. They can physically cause blockages. Some worms, like roundworms, can be as fat as a pen and as long as a ruler. Tapeworms in a horse are like pumpkin seeds that like to hang out together. These create actual traffic jams in your horse. This can lead to colic.


  • Diarrhea and other digestive problems are also likely. Worms that have part of their life cycle in your horse’s lungs (I’m looking at you, ascarids and lungworms) can lead to coughing and other respiratory problems.


  • Worms in a horse also like to take your horse’s nutrients. This can result in a poor coat, performance issues, and just generally feeling bad. If your horse is young and growing, this critical growing stage can be impaired by a large parasite load.


  • It’s true that horses will always carry parasites. But their load needs to be maintained at a safe level, which is why you need to monitor your horse twice yearly, spring and fall with fecal egg counts (FEC).


****If you need to take a moment and wretch, please do so! Worms are sorta gross.***


thoroughbred mare and foal in paddock

Young horses are especially susceptible to worms and parasites.


How do you measure a horse’s parasite load?


  • The fecal egg count (FEC) can give you a rough idea of your horse’s parasite load. The FEC is an easy and inexpensive test that quite simply, takes some of your horse’s manure and looks for worm eggs on the microscopic level. tells us:


“The parasite load or worm burden can be used to classify your horse into a shedding or contaminator category. The American Association of Equine Practitioners (AAEP) Subcommittee’s Parasite Control Guidelines classifies horses into three different levels of egg shedding categories – Low, Medium and High. A horse with a fecal egg count between 0 and 200 EPG is classified as a low shedder. A medium or moderate shedder has an EPG between 201 to 500 EPG, and a high shedder has an EPG above 501 EPG.


The more fecal egg count tests performed on your horse the more confident you can be about its shedder classification. For example, if multiple fecal egg count test results consistently yield between 0 and 200 EPG, then you could consider your horse as a low shedder. Recent research, suggests that over time, a horse tends to stay in the same shedder category.”


fecal egg count test to mail in

You can now mail your horse’s poop for a fecal egg count test. Oh, what wonderful times we live in.


What do the results of a FEC mean for deworming your horse?


  • If your horse turns out to be a low or medium shedder when you do a FEC in the spring and fall, you may not need to deworm your horse. High shedders are usually the ones to target with dewormers that are specific to the results of the fecal egg count.


  • It’s always best to test all of the horses on a farm at the same time, especially if they share pastures or paddocks. The high shedders should be dewormed and a second FEC should be done about two weeks later to check on the effectiveness of the dewormer that you used.


  • Now – getting back to how horses get parasites. Your horse eats eggs or larvae of intestinal parasites in the pasture or paddock. Some parasites, like bots, have a different life cycle, but they still manage to get into your horse’s body. Think of it like wormy salt on your horse meals?


dewormer options at the store

These dewormers only work if you know what your horse has growing in his belly.


How can you reduce your horse’s parasite load?


This is a three-step process – testing, deworming with your veterinarian’s guidance, and maintaining your horse’s environment.




“Keeping your horse’s stall, pasture and dry lot, clean year round is critical for preventing parasitic reinfection. Considering most horses become infected while grazing, proper care of your paddocks, pastures, and fields is a vital but often overlooked – aspect of any effective parasite control program. To reduce your horse’s parasite exposure:


  • Clean regularly – remove and dispose of manure at the very minimum three times per week.


  • Rotate pastures – move horses between pastures to prevent re-exposure to parasites


  • Reduce pasture load – fewer horses per acre means less chance of consuming parasites


  • Use elevated feeders – lift grain and hay off of the ground where parasites thrive


  • Mow pastures – taller grass shades parasites from direct sunlight and helps them hold moisture.


  • Additionally, practicing proper pasture management will decrease reliance on chemical dewormers.


Keeping your horse free of harmful parasites is a critical step in keeping your horse healthy. Therefore, it is important to develop a parasite control program specifically designed for your horse that targets and controls worms and stomach bots, as well as prevents their reoccurrence.”


picking up manure in a pasture



Letting manure sit in your pastures is a sure-fire way to keep the parasites part of your horse’s life.


  • If you just drag the pastures, you are probably doing a fine job of just spreading parasite eggs around.


  • BUT – if you know you are fighting parasites that can’t survive a freeze, drag the empty pasture to spread piles around before a deep freeze. Some parasite eggs are fine in a freeze, but will die in hot and dry conditions.


  • Your barn’s climate and your horse’s parasites will tell you when to do this. A bit of research and a call to your local Ag Extension service can help you here, too.


But what about pasture management?


  • If your pastures are eaten down to the earth, your horse is more likely to eat parasite eggs and larvae. Larvae like to live at the base of plants and grasses, so move horses to a new pasture before the grass gets too short.


  • And speaking of short grass – this stuff is super tasty to horses, as the shorter length signals the grass to store sugars in order to grow. So horses are likely to munch this stuff to the ground.

A conspiracy between grass and parasites?


  • If you want to spread manure into pastures for fertilization, you need to compost it first. Composting to proper temperatures, about 140F, for a few days at least will kill parasite worms. Then you can spread the manure in your pastures.


So yes. Containing your horse’s parasite load is a bit more than doing fecal egg counts and popping some dewormer when necessary. You need to get into the paddocks and scoop the poop. You need to rotate pastures and keep things mowed. Most importantly, make sure you know what parasites are in your horse and what the life cycle of that parasite is, so that you can take care of your horse’s pasture. Your best resource will be your vet and your local Ag Extension service to help you figure out the best ways to get your farm’s parasites under control.


And that concludes today’s discussion about worms and poop and pastures!


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