Your Informative Guide to Deworming Horses

Knowing how often a horse should be dewormed and which deworming products work the best is a question that many horse owners likely find themselves asking. This informative guide to deworming horses will explain:

• How horses get worms and why you should deworm your horse
• How often you should deworm your horse
• What types of worms horses can get infected with
• Which dewormer gets ride of worms in horses
• Which months to deworm a horse and a recommended deworming schedule for horses
• How to know if you horse has worms

As many horse owners already know, equine parasites and worms can cause an array of health issues with horses if left untreated. You can reduce these risks by utilizing a modern deworming program using fecal egg count tests combined with targeted deworming or using a traditional rotational deworming schedule.

How Do Horses Get Worms and Why Should You Deworm Your Horse?

Horses can get worms from being turned out in a pasture contaminated with parasitic worms from other horses’ manure or by flies laying their eggs on a horse’s coat.

When horses get worms from being turned out in a pasture that’s contaminated, it normally means manure from an infected horse mixed with the grass and soil, resulting in eggs, larvae, and adult worms just waiting for your horse to graze and ingest them. Horses can get different types of worms from other infected horses or even reinfect themselves from their own manure in the field!

So, what if your horse lives alone, they can’t get worms, right? Wrong! Some worms, such as Bots, come from adult flies laying their eggs on a horse’s coat, especially around the legs. A horse then ingests them and voila, those fly babies have hit the road along your horse’s digestive tract.

You should deworm your horse because horses can suffer from a variety of health conditions caused by a high load of parasites, as each species of parasite can affect different parts of their bodies. For example, Strongyles may cause damage in the digestive tract while Ascarids spread around to the liver, lungs, and throat. It is important to deworm your horse to prevent serious health problems that worms can cause, whether minor issues such as poor coat quality to more serious concerns like colic or internal damage.

How Often Should You Deworm Your Horse?

Traditionally, horse owners will follow a rotational deworming schedule dependent on the time of year that certain worms are more active, giving their horses a rotation of different dewormers every other month, year-round. Deworming programs are not always a simple answer and can often be a hot topic of debate on which program works the best.

However, more research has been done to show that many parasites are becoming resistant to some of the active ingredients used in deworming products, which has created a more modern take on a deworming program by using Fecal Egg Count tests (FEC) and only giving a dewormer based on those FEC results.

Fecal Egg Count tests are simple and affordable tests done by your veterinarian or a lab, where they will examine a manure sample under a microscope. The results will look something like “100 eggs per gram (EPG)”. The number will tell you if your horse has a low, medium, or high parasite load, also resulting in the number of parasites they are shedding every time their manure hits the ground. An EPG count over 500 is considered a higher level and would tell you that you should give your horse the appropriate dewormer to kill off some of the worms in their system.

If your horse has a low EPG count, you can just give a dewormer in the spring and/or fall. A moderate EPG (200-500) would call for adding in one more deworming treatment during the summer. A high EPG (>500) would warrant up to four deworming treatments that year, including one in the fall after the last hard frost. Young horses and foals may require a different or more frequent deworming program so consulting with your vet first is always recommended.

What Types of Worms Can My Horse Get?

There are four main species of internal parasites that horses can get infected with, Strongyles (Red Worms or Blood Worms), Tapeworms, Ascarids (Roundworms), and Bots. Each worm being a little different with how they develop, the damage they can cause, and the time of year they are most active.

1. Strongyles (Red Worms or Blood Worms): Strongyles infect horses after a horse eats the larvae. They develop into adult parasites while they make their trek through the intestines, causing colic, enteritis, anemia, weakness, emaciation, or diarrhea.
2. Tapeworms: Nearly all horses will be exposed to Tapeworms at some point, typically young or older horses. These infestations don’t often show any outwardly clinical signs but can cause damage in the digestive tract. They do not appear on Fecal Egg Count tests. Products such as Zimecterin Gold and EquiMax will also kill off tapeworms, making those dewormers a great option to do at least once a year, in the spring and/or fall.
3. Ascarids (Roundworms): Many young horses suffer from Roundworms as their bodies don’t always have the immunity needed to fend them off in their early life. These worms begin their life in the intestines but go exploring and find their way in the liver, lungs, and throat. Heavy loads of roundworms can cause a pot-bellied look, poor coat, weight loss, colic symptoms, and even stunt a developing horse’s growth.
4. Bots: You have likely seen these during the summer months and may not have even realized what they were. Bot eggs start out as tiny yellow dots sprinkled across your horse’s legs, chest, and neck, after an adult-fly lays them there. These eggs will then get ingested from a horse grooming or biting at themselves during fly-season, where they eventually make their way into the stomach lining. They can stay there for 8-10 months before the larvae will pass through into manure and start the circle of life all over again

What Type of Dewormer Removes Worms?

The main type of dewormers that remove worms in horses are Febedazole, Oxibendazole, Ivermectin, Moxidectin, Pyrantel Pamoate, Pyrantel Tatrate, and Praziquantel.

There are many popular dewormers for horses on the market, while most of them come in paste form, making it easy to measure the correct dose based on the weight of your horse. After discussing with your veterinarian, you can determine which product would work best either based on Fecal Egg Count test results, or the rotational schedule you choose.

Here is a breakdown of what types of dewormers work on different parasites in horses:

Combining deworming products with an effective management system around your farm can help reduce the number of worms your horse is exposed to. These are some great ways reduce or prevent the number of parasites at your farm:

1. Manage Pastures: Remove manure when possible, or mow/harrow pastures to break up manure piles which exposes them to predators such as birds and small mammals or rodents. Doing this weekly can greatly decrease egg and larvae populations.
2. Pasture Rotation: Move horses from different pastures, allow some pastures to rest for at least a few months, and try to keep the number of horses in each pasture low.
3. Deworm Your Horses: On either a rotational program or based on annual or semi-annual Fecal Egg Count tests.

What is a Good Deworming Schedule for Horses?

A good deworming schedule includes rotational deworming, where you rotate the different types of dewormers to ensure you’ve covered all types of worms at the ideal times of the year. Here is a great example of a horse deworming rotation chart based on the target active ingredient in the deworming products:

How Do I Know If My Horse Has Worms?

Some of the most obvious signs that your horse has worms are:

• Dull coat
• Tail rubbing
• Itchy skin
• Weight loss
• Diarrhea
• Poor performance
• Colic
• Poor body condition
• Lethargy
• Lack of appetite
• Pot-bellied apperance

Horses almost always have some level of internal parasites in their system, it’s just a matter of how many and how long they’ve had them, before they start causing health problems.

Having your veterinarian do a physical exam along with a Fecal Egg Count and/or blood test can tell you if your horse has worms and which deworming product would be necessary to remove those worms before they cause physical harm to the horse. We always encourage you to consult with your veterinarian when it comes to the health of your horse, but rest assured following these helpful tips under your veterinarian’s guidance should have you well on your way to a healthy, parasite-free horse and farm before you know it!

Disclaimer: This helpful guide to deworming horses is for informational use to help you better understand worms and parasites in horses and how they can be managed, but is not intended to treat, cure, or diagnose any medical conditions or treatments for your horse. Please consult with your veterinarian with any questions regarding your horse’s deworming program.