Worming Your Horse: What Type Of Wormer To Use & When

Worms are a serious problem for horses. Horses consume grass and hay that can have worms in it – so all horses have worms. The issue comes when an infestation happens, which can lead to weight loss, an inability to gain weight, bloating, lack of nutrition, bad hooves, and overall bad condition and other serious health issues. Keeping your horse on a routine worm schedule is the best way to handle worms and to make sure your horse is healthy. Knowing when to worm and which wormer to use based on the season and presence of worms on the ground can be tricky to navigate and confusing. Use this guide by ESA to help you know what wormer to use and when!

How Often Should I Worm My Horse?

The best way to find out if your horse needs to be wormed is to get a fecal test done by your vet. While fecal tests are always preferred, having a general worming schedule is a way to make sure that your horse has the best chances against a worm infestation.

  • Low: Less than 200 Eggs Per Gram (of manure)
  • Moderate: Between 200 – 500 Eggs Per Gram
  • High: More than 500 Eggs Per Gram

*If you don’t know what type of shedder, the safest bet is to assume your horse is a moderate shedder.

Worming Schedule For a Low Shedder – Worm 2x a Year

Spring (March/April) use Ivermectin or Moxidectin – any of these wormers:

Fall (September/October) use Ivermectin with Praziquantel or Moxidectin with Praziquantel – any of these wormers:

Worming Schedule For a Moderate Shedder – Worm 3x a Year

Follow the same schedule as above in Spring and Fall, and add in another worming in the summer (July). Use Pyrantel Pamoate or Fenbendazole- any of the following:

Worming Schedule For a High Shedder – Worm 4x a Year

Follow the same schedule as above in spring, fall, and summer, and add in another worming in the winter (December). Use Oxibendazole – this wormer in the winter:

Important Things To Know About Worming

Worming your horse is important, as they commonly destroy your horse’s organs and cause serious, sometimes fatal, health issues. So, making sure you are worming your horse at least 2x a year is necessary for maintaining his health.

Type of Worms

There are many different parasites that are in the grass and hay that your horse is eating; your horse is at risk for getting many different types of worms. Dewormers will only work to eliminate the specific type of worms that it is meant to kill. This is why following the rotation of the wormers is important because if you continuously worm for one specific type of worm, your horse will likely get an infestation of the other worms that you are not worming for.

Here are some of the most common types of worms in horses:

Pinworms in Horses

Your horse can pick up pinworm eggs from bedding, water, and feed. They can also be exposed to the eggs from brushes or grooming materials, a tail wrap, or even inside the stall or on fencing. If another horse has these worms, your horse will likely get them. These will cause your horse to have itching around his rear end.

Tapeworms in Horses

Tapeworms are one of the most common types of worms. Horses will pick them up while they are grazing, as they will pick up mites from the plants. From there, they will stay inside their intestine and are able to live off the food. The most common symptoms of tapeworms are mild colic and diarrhea.

Bots in Horses

You’ve likely seen the evidence of bot flies, as we do our best to use a bot knife and remove the eggs from our horse’s legs and bodies during the warmer weather. After the eggs are laid on their bodies, horses can ingest the eggs when they lick themselves. These parasites will also live in the intestine and can cause mild colic and poor health.

Ascarids or Roundworms in Horses

These worms are some of the most dangerous, especially to foals and horses under the age of two. This is because ascarid larvae migrate into the blood vessels and go into to horse’s the lungs and liver when ingested. Like most worms, these worms will live in the small intestine. Since the larvae goes through the lungs, many young horses suffer from a respiratory disease, colic, and have a hard time gaining weight.

Bloodworms (Small and Large Strongyles) in Horses

These worms are Ingested by horses when eating grass in pastures. The blood worm eggs will hatch and climb on the grass blades where they are then swallowed by the horse when grazing. Both old and young horses are at risk for these worms to burrow into their intestines, which cause diarrhea, colic, weight loss, and a general overall poor condition.

Then, once the bloodworms mature, they are very dangerous. They will damage organs and weaken a horse’s abdominal artery walls. The most common symptoms include colic, weight loss, and diarrhea.

Threadworms in Horses

Threadworms are another worm that is highly dangerous, especially to foals and young horses. These young horses can be infected when nursing from their infected mother with larvae. From here, the worms live in the intestinal tract, causing weakness and diarrhea in young horses.

Age of the Horse Matters When Worming

Foals need to be dewormed initially at 1 – 2 months of age. After that, you’ll want to continue worming this foal every 30 – 60 days until he/she is 1 year old. Then, once your foal hits a year old, he can move forward with a routine worming schedule, as discussed above.

The Types Of Medication and What Worms They Kill

Moxidectin Paste and Praziquantel

Removed and control small and large strongyles, pinworms, ascarids, stomach worms, hairworms, and bots.

Ivermectin Paste and Praziquantel

Removes and control small and large strongyles, hairworms, pinworms, lungworms, stomach worms, bots, and ascarids.

Pyrantel Pamoate

Removes and control small and large strongyles, pinworms and roundworms.


Removes and controls small and large strongyles, pinworms and ascarids.

Pyrantel Tartrate (Daily Dewormers)

Provides continuous protection from small and large strongyles, pinworms and ascarids.

Horse’s Weight and Dosage When Worming

You will want to have an accurate weight estimate for your horse to determine how much wormer your horse needs. Each wormer has specific instructions on it that will let you know how many grams your horse needs. Read the instructions carefully so that you do not under or overdose. Check with your vet if you have any specific questions about these wormers or dosage.