The Modern Guide to Horse Deworming

A proper deworming program for adult horses should be designed for the entire herd, not just individual horses. Information is gathered from the individual horse, and parasite fecal egg counts are performed to test whether the horse is a low, medium, or high strongyle parasite shedder. With this information in hand, the horse owner can then work with their veterinarian to decide what dewormer to use when.

Why Deworming is a Smart Choice

If you’re like any other horse owner who wants to take great care of their horse, the idea of your horse carrying a high load of parasites is enough to make you cringe. But it is important to remember that it is completely normal for horses to have parasites and that the overwhelming majority of horses are perfectly happy and healthy with their parasites. However, in rare cases, a high parasite load can cause poor quality coat, weight loss, diarrhea, or colic.

Horses get infected with parasites, but it doesn’t happen exactly like getting infected with a contagious disease like influenza or rhino (Equine Herpes Virus). Horses usually get worms when they’re turned out in a contaminated pasture. A horse can even re-infect himself with his own intestinal worms.

Fortunately, there is more you can do than cringe when it comes to parasite control. Along with using proper environmental management to reduce parasite transmission (like regularly removing manure from pastures – not spreading it!), you can help reduce the parasite infection pressure with a proper deworming program.

How to Deworm Your Horse

Deworming may be something you’ve been doing the same way for as long as you can remember—most likely rotating between ivermectin, pyrantel, fenbendazole, and a handful of different products about every eight weeks or so. However, as drug resistant parasites and the lack of new dewormers in the pipeline become increasing concerns, more and more horse owners, barn managers, and veterinarians are rethinking the way they deworm horses.

Nowadays, the strategy against parasites takes a concerted effort consisting of a baseline of treatment administered to all horses in the herd, with additional treatments provided to the higher strongyle parasite shedders. The baseline treatments are put in place to control large strongyles and tapeworms, or the “non-cyathostomin” parasites (“cyathostomin” parasites being small strongyles). Additional targeted treatments are applied to bring down the infection pressure of cyathostomin parasites.Luckily, developing a meaningful deworming program is easier than it sounds! Here, we’ll walk you through the best practices for creating a good deworming program.

Your first step in developing your horse’s deworming program is to have a fecal egg count (FEC) test performed. Ideally, you should try and coordinate this so you get all herd members following the same program. Because your results will help you make the most appropriate choices for your horse, a good time to get your fecal egg count test run is in the spring when parasite transmission season is about to start.

A fecal egg count measures the number of strongyle eggs your horse is passing in each gram of his manure. When you send a sample to your veterinarian or independent laboratory, you get back a number like 50 EPG (eggs per gram) or 500 EPG. That number tells you whether your horse is a low, medium, or high parasite egg shedder, which in turn helps you understand how to develop your horse’s deworming plan.

If your fecal egg count test comes back less than about 200 eggs per gram (of feces), then your horse is likely a low egg-shedder and only needs to be dewormed twice a year. If the results show more than 500 eggs per gram, then your horse is likely a high egg-shedder and needs to be dewormed more often. Depending on region and climate, high shedders can be dewormed additionally in the middle of summer or later in the fall.

Keep in mind that even if your horse’s fecal comes back negative, that doesn’t mean your horse is parasite-free. Because horses are grazers, they’ll never be completely free of parasites. So, your horse with a negative fecal still almost assuredly has intestinal parasites, but those parasites simply aren’t shedding enough eggs to make it above the detection limit of the test.

Once you know whether your horse is a low, medium, or high shedder, you can work with your vet to set your deworming schedule and decide what dewormer to use and how often. Targeting your horse’s specific deworming requirements is the key takeaway, and those factors will vary quite a bit based on how heavy an egg shedder he tends to be, your geographic location, the age distribution among the herd members, the stocking density and pasture quality, and the manure management on your farm. That’s why experts no longer recommend a “one size fits all” approach!

After you’ve put your deworming plan into action, it’s a smart idea to perform second fecal egg count test 10 to 14 days after deworming to check the treatment effects. This is called a fecal egg count reduction test and it is recommended to include at least 6 horses in the test, if available. Scientists are discovering more and more resistance to commonly used dewormers, so it’s important to make sure there are actually less eggs in your horse’s manure after the deworming.

And that’s it! Creating a targeted deworming plan for your horse really is easier than it sounds at first. In actuality, it really is less work, less expensive, and more effective than the rotational deworming program of the old days. By following the simple steps we outlined above, you’ll have a targeted deworming program for your horse in no time!

Courtesy of SmartPak