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How Often Should You Worm A Horse?

There are as many different theories of horse deworming as there are horsemen and equine veterinarians. There are also a great many different types of internal parasites. It’s no wonder that the deworming process can seem confusing. In this article, we explore the topic of equine deworming and provide good advice on how and when you should worm your horse. Read on to learn more.

How Common Are Intestinal Parasites In Horses?

Parasite infestation is the very most common of equine diseases. That’s why it is so important to set up and follow a regular schedule of deworming. Consistent treatment eliminates existing infestation and prevents reoccurrence. Keeping your horse parasite free is not really possible, but regular treatment combined with good stable and pasture maintenance can greatly reduce intestinal worm problems in horses.

What Are The Factors That Affect Worm Load In A Horse?

Every horse is an individual, and every situation is different, so the factors that affect a horse’s worm load are many and varied. A group of horses sharing a pasture or stable and receiving exactly the same care may have very different levels of infestation. This is why every deworming program must be carefully devised to take all potentially affecting factors into account. Here are just a few:

  • Pasture-mates: Other horses, donkeys, mules, goats, cattle, sheep and other animals in the pasture may be carrying parasites may be transferred to your horse.
  • Travel: Horses who are taken from place to place and shown, worked or raced with other horses have greater chance of being exposed to horses who are infected.
  • Pasture load: When horses graze in an area, parasite exposure is increased by the presence of droppings.
  • Age: Some parasites are far more common in younger horses, from foals to yearlings.
  • Location: Different sorts of parasites thrive in different climates and regions.
  • Season: Some parasites (e.g. bot flies) have very short seasons of activity.

Even when all of these factors are considered, it’s important to remember that different horses carry different worm loads. Some research has indicated that in some instances, only twenty percent of horses in a herd may be responsible for eighty percent of the parasite problem.

How Can You Identify Your Horse’s Deworming Needs?

horse's deworming needs

Be sure that your horse’s annual exam includes a fecal test. Using this test, your vet can determine whether worm eggs are present in your horse’s manure and determine the extent of the infestation. Once a fecal egg count has been conducted, your vet will work with you to set up just the right program of targeted deworming.

Ten-to-fourteen days after the first deworming treatment, it’s smart to do another fecal egg count. This will help you evaluate how effective your treatment has been. Sometimes worms develop a resistance to certain products, and this causes incomplete results. When this happens, you may need to try again with a different product.

How Do Worms Develop Dewormer Resistance?

It used to be common practice to deworm every couple of months, but now we understand that this schedule may actually help parasites develop resistance to deworming products. This happens when the product kills off the weaker members of the parasite population and the strong survive.

These stronger parasites have traits that allow them to resist poisoning by specific products, and they pass these traits on to their offspring. To prevent this problem, vets now recommend deworming less often and rotating products to prevent the development of resistance.

What Are the Best Strategies For Deworming Horses?

best strategies for deworming horses

It can be difficult to hit just the right balance between to keep your horses relatively worm-free while avoiding strengthening the parasites. One option is to routinely deworm all the horses on your premises in the springtime and again in the autumn using moxidectin or ivermectin with praziquantel added.

Conduct fecal egg counts during the season when horses are most likely to pick up parasites in your area. This varies from place-to-place. For example, in the United States, parasite transmission is more common during the winter in the southern states and during the summer in the northern states.

Find out when the most active parasite season is in your area and have fecal count tests conducted. When you have the results, worm the horses with high worm loads using a completely different deworming product. Consult your veterinarian to determine the best horse dewormer for your situation.

How Often Should Fecal Egg Counts Be Conducted?

Conducting a fecal egg count annually can help you identify whether the parasites you are targeting have developed resistance to your treatments. All horses will have some worm eggs present in every fecal egg count. You will never have a worm-free test.

It is also important to understand that some horses typically have a greater potential for infestation than others. For example, horses that are stressed because of frequent travel, a heavy workload, ill health, chronic conditions or advanced age may have a higher worm load. Foals and younger horses are also more susceptible to worm infestation. For these horses, it’s may be a good idea to conduct frequent fecal egg count tests and to deworm them several times a year.

Are There Any Daily Deworming Products?

Daily deworming is possible through the use of convenient feed additives that provide constant protection against parasites. With regular use, these products kill existing infestations and prevent further infestation.

The active ingredient in daily dewormers is pyrantel tartrate. This substance kills worm larvae before they can mature, reproduce and move into your horse’s body tissues, causing internal organ damage.

Using a daily dewormer also breaks the life cycle of the parasite by causing horse manure to become inhospitable to the parasite’s eggs. Using a daily dewormer along with a bi-annual broad spectrum worm treatment provides very complete control of parasites.

The one caveat of using a daily dewormer is that you must provide the recommended dose every day. Consistency is very important because missing doses causes the level of deworming product in your horse’s system to decline. This may cause parasites to develop resistance to the product.

Are There Natural Worm Deterrents?

natural worm deterrents

In addition to commercial deworming products, there are some natural supplements you can use that may be helpful in reducing worm infestation. About three ounces of food grade diatomaceous earth added to your horse’s feed daily may help reduce worm infestation and makes manure inhospitable to worm and fly larvae. A tablespoonful of powdered sulfur added to feed daily may also help reduce worm infestation and reduces your horse’s appeal to flies. Keeping a sulfured salt block available may also be helpful.

It is important to note that information regarding the effectiveness of these natural remedies is anecdotal and that these products should not take the place of chemical deworming products. DE and sulfur are safe supplements that may help support your deworming efforts and are beneficial in helping your horse maintain overall good health.

Good Practices Help Reduce Exposure To Parasites

No matter how often you deworm your horse or what method you choose, it is important to understand that parasites thrive in unclean conditions. If you let manure pile up in your pasture, paddocks and stalls, you are going to have a parasite problem. For this reason, it is very important that you keep manure cleaned up.

Follow these six guidelines to reduce your horses’ exposure to intestinal worms:

  1. Rake up and properly dispose of manure a minimum of two times every week.
  2. Harrow your pastures seasonally to break up piles of manure and expose larvae and eggs to the elements.
  3. Rotate your horses from one pasture to another on a regular basis to help break up the parasites’ life cycles.
  4. Group your horses by age to maximize the effectiveness of your deworming efforts.
  5. Don’t overcrowd your pastures because more horses means more manure, which means more parasite presence.
  6. Never feed on the ground as that is where parasites thrive. Always feed hay and grain in elevated feeders.

What’s The Bottom Line?

Parasite control is a multi-pronged process. You will never be able to keep your horse completely free of parasites, but if you keep your premises clean, perform regular fecal egg count testing and use good deworming products on a regular basis as determined through consultation with your vet, you should be able to keep equine worm infestation under control.

Ask The Vet – When Should You Deworm Your Horse?

Nicky Ellis
Nicky has been an editor at Horses & Foals since 2017. Horses have been in her life from her earliest memories, and she learned to ride a horse when she was 5. She is a mom of three who spends all her free time with her family and friends, her mare Joy, or just sipping her favorite cup of tea.


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