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Horse Parasites: Effective Prevention and Control Methods

Horse parasites are a common issue faced by horse owners and caretakers around the world. These internal parasites can have detrimental effects on the health and well-being of horses, leading to various symptoms and complications if left untreated. It is crucial for those involved in equine care to understand the different types of parasites, their life cycles, and how to effectively diagnose and treat them to ensure the overall health of their horses.

There are several types of internal parasites that can affect horses, including worms, insects, and microscopic organisms. Some of the most prevalent equine parasites include strongyles, ascarids, tapeworms, pinworms, bots, and threadworms. These parasites can cause a variety of symptoms, ranging from weight loss and dull hair coats to colic and lethargy. As a horse owner or caretaker, being able to recognize the signs of parasitic infection is vital for a prompt diagnosis and appropriate treatment.

Early intervention and prevention measures are crucial in minimizing the impact of horse parasites. By following recommended deworming schedules, monitoring your horse’s environment, and regularly consulting with a veterinarian, you can help protect your equine companions from the negative effects of parasitic infection.

Key Takeaways

  • Horse parasites are a common issue, and a proper understanding of them is vital for overall equine health.
  • Types of internal parasites include strongyles, ascarids, tapeworms, pinworms, bots, and threadworms.
  • Early intervention and prevention methods, such as deworming and monitoring, are crucial in combating horse parasites.

Understanding Horse Parasites

Horses, like all animals, can be affected by various parasites. These internal parasites can cause a range of health issues in horses and need to be properly managed to ensure the horse’s well-being. Common parasites affecting horses include worms, insects, and microscopic organisms. In this section, we will discuss some of the most common types of parasites found in horses.

Strongyles, also known as bloodworms or redworms, are a common type of intestinal parasite found in horses. These worms come in small and large forms, and both types can cause serious health problems. Small strongyles are particularly prevalent, and any grazing horse is likely to have some degree of infection.

Another common type of horse parasite is the ascarid, or roundworm. These worms can be particularly harmful, especially to young horses, and are known to cause respiratory problems and intestinal blockages. It is critical to maintain a proper deworming regimen to control ascarid infections.

Pinworms are another type of intestinal parasite that affects horses. While pinworms generally do not cause severe health issues, they can cause discomfort and irritation around the horse’s tail, leading to excessive tail rubbing and potential secondary infections.

Some other common equine parasites include:

  • Tapeworms: These flat, segmented worms can affect various parts of a horse’s intestine and can cause weight loss, colic, and other digestive issues.
  • Stomach Bots: These are actually the larvae of a fly species that lay their eggs on a horse’s legs and hair. The larvae are ingested as the horse grooms itself. Once inside the stomach, they can cause ulceration and lead to poor appetite and weight loss.

Types Of Horse Parasites

Internal Parasites

Horses can be affected by a variety of internal parasites. Some of the most common ones include worms (helminths), insects (arthropods), and microscopic organisms (protozoa)1. Among these parasites, strongyles, ascarids, tapeworms, pinworms, bots, and threadworms are frequently found in horses2.

  • Strongyles are a type of roundworm that can cause digestive issues and anemia in horses.
  • Ascarids, another type of roundworm, can lead to weight loss, poor coat condition, and colic.
  • Tapeworms are a less common but still clinically significant parasite, primarily affecting adult horses3.
  • Pinworms cause itching and discomfort around the horse’s anus and can result in tail rubbing.
  • Bots are the larvae of a type of fly that infests the horse’s stomach and can cause digestive problems.
  • Threadworms are small worm-like parasites that can cause diarrhea, especially in foals.

External Parasites

In addition to internal parasites, horses can also be affected by external parasites, also known as ectoparasites4. Some common external parasites include:

  • Lice: These tiny insects can cause itchiness and hair loss in horses. There are two types of lice that can affect horses: biting lice and sucking lice.
  • Mites: Mites are small arachnids that can cause skin irritation and inflammation. They typically affect the horse’s legs, face, or ears.
  • Ticks: Ticks are blood-sucking parasites that attach themselves to the horse’s skin. They can transmit various diseases, such as Lyme disease and anaplasmosis.
  • Flies: Various species of flies can bother horses, causing irritation and potentially transmitting diseases.

Horse owners should be aware of these common parasites and take appropriate measures to prevent and control infestations, as well as monitor their horses for signs of infection.


  1. Intestinal Parasites in Horses

  2. Prevalent Parasites: Common Types of Equine Internal Parasites

  3. 9 Most Common Internal Horse Parasites

  4. Different Types of Horse Parasites

Symptoms Of Horse Parasites

Horses can suffer from various internal parasites such as worms, insects, and microscopic organisms. These parasites can lead to a range of symptoms, depending on the type and severity of the infestation. This section will focus on the most common signs that a horse may have a parasite problem.

Weight loss is often an early indicator of internal parasites, as they compete with the horse for nutrients and can cause damage to the intestinal lining. A horse suffering from a parasite infestation may show poor growth, especially if it is young. Further, the animal’s coat can become coarse and dull, indicating poor overall health.

Another telltale sign of parasite infestation in horses is the development of a potbelly. This occurs when the parasites cause inflammation in the horse’s intestines, leading to abdominal distension [1]. A horse with parasites may also experience excessive tail swishing or scratching, as some parasites can cause irritation around the animal’s anal region.

In addition to these external signs, intestinal parasites can lead to various types of colic in horses. Colic is a general term referring to abdominal pain, which can be caused by a variety of factors, including internal parasite infestations. Horses infested with ascarids, for example, may suffer from diarrhea [2].

Suboptimal performance and decreased stamina can also result from parasitic infections. Horses with a high parasite burden may struggle to perform at their best and may not be able to maintain their usual exercise routines.

In summary, if a horse exhibits weight loss, poor growth, a dull coat, a potbelly, tail swishing or scratching, colic, diarrhea, or reduced performance levels, it may be suffering from a parasite infestation. Prompt diagnosis and treatment are crucial to maintain the horse’s overall health and well-being.

Diagnosing Horse Parasites

Clinical Examination

A thorough clinical examination is crucial in diagnosing horse parasites. Veterinarians should assess the horse’s general condition, including its weight and appetite. If a horse appears thinner than usual but continues to eat regularly, parasites may be the cause. Accurate weight estimation is achieved by using a weight tape or a tape measure.

Diagnostic Tests

Several diagnostic tests are available to identify and quantify parasites in horses. The most common methods include:

  1. Fecal flotation: This test helps identify the type and quantity of parasites present by detecting parasite eggs in the manure. The fecal flotation technique is widely used due to its accuracy and simplicity. Learn more about fecal flotation in the UC Davis School of Veterinary Medicine article.
  2. Fecal egg count (McMasters) testing: This test determines the number and kind of parasite eggs in a horse’s feces, providing valuable information for creating a targeted deworming plan. The AAEP Internal Parasite Control Guidelines provide additional information on FECRT and the appropriate steps to follow.
  3. Culture of feces for infective larvae: This method involves growing infective larvae from fecal samples, allowing for the identification of specific parasites present in the horse’s gastrointestinal tract.

When diagnosing horse parasites, it is essential to utilize accurate diagnostic methods, as overuse of deworming medications in recent decades has led to drug resistance in many parasite species.

Preventing And Treating Horse Parasites

Controlling internal parasites is essential for maintaining the health of horses. It involves using anthelmintics as well as incorporating proper management practices, such as pasture management and stable environment.


Deworming is the primary method of controlling internal parasites in horses. It involves administering anthelmintics, which are drugs that help eliminate parasitic worms from the animal’s digestive system. There is, however, an increasing concern about parasite resistance to dewormers. To minimize this issue, it’s recommended to use different classes of anthelmintics and practice proper pasture management.

To develop an effective deworming schedule for each horse, consider factors like age, stabling conditions, and the horse’s overall health. Moreover, it’s essential to conduct fecal egg counts to determine which horses require treatment. It’s crucial to consult with your veterinarian when establishing a deworming strategy tailored to your horse’s specific needs.

Pasture Management

In addition to deworming, proper pasture management plays a critical role in preventing parasitic infections. Horses often become infected with intestinal parasites when they eat grass or hay contaminated with manure containing parasite eggs or larvae.

To reduce the risk of infection, follow these pasture management practices:

  • Rotate pastures: Regularly move horses between pastures to avoid overgrazing and reduce the chances of parasite exposure.
  • Manure removal: Clean pastures periodically by removing manure to prevent the buildup of parasite eggs or larvae.
  • Mixed grazing: Introduce other grazing animals like sheep or cattle to your pasture. They can consume different parasites than horses, in turn, disrupting the parasite lifecycle.
  • Resting pastures: Allow pastures to rest for a few months by not grazing horses on them, during which time parasite eggs may die before they find a new host.

Implementing a comprehensive parasite control program that includes deworming and proper pasture management can effectively prevent and treat horse parasites, enhancing the health and well-being of the equine population.


Equine parasites are an important health concern for horse owners and managers. A thorough understanding of the common types of internal parasites that infect horses, such as strongyles, ascarids, tapeworms, pinworms, bots, and threadworms, is vital for maintaining the health and well-being of horses. Effective management strategies should be informed by a knowledge of parasite life cycles and the specific symptoms they cause.

Intestinal parasites typically infect horses through the consumption of contaminated grass or hay. As each type of parasite exhibits different signs of infection, it is crucial to monitor horses for any abnormal behavior or physical symptoms. In some cases, infected horses may not show any signs at all. Regular veterinary check-ups and fecal examinations are essential for early detection of parasite infections.

Implementing whole-farm management strategies can significantly reduce the parasite load in horses. While not every technique may be applicable to all farms, adopting as many strategies as possible can help improve horse health. Management practices should focus on deworming, rotational grazing, proper pasture maintenance, and reducing overcrowding to combat parasite infections effectively.

In summary, understanding common equine parasites and employing comprehensive management strategies help protect horses from various internal parasitic threats. Regular monitoring and veterinary consultations will further ensure a healthier environment for both the horses and the people who care for them.

Frequently Asked Questions

What are common symptoms of internal parasites in horses?

Horses infected with internal parasites might exhibit various symptoms depending on the type of parasite. These can include weight loss, diarrhea, poor coat condition, and colic. However, some horses may not show any signs of infection.

How can I identify different types of equine parasites?

Identifying specific types of equine parasites typically requires a fecal egg count test, which is conducted by a veterinarian. This test involves examining a small sample of the horse’s feces under a microscope to determine the presence and types of parasite eggs.

What are the most common types of worms found in horses?

The most common types of worms found in horses are small strongyles, large strongyles (bloodworms), tapeworms, roundworms (ascarids), and threadworms. While large strongyles were previously the greatest threat to horse health, modern deworming practices have made them more manageable.

How do horses acquire parasites and how can they be prevented?

Horses usually acquire parasites by consuming grass or hay contaminated with manure containing parasite eggs or larvae. To prevent infection, it’s crucial to maintain a clean environment with proper pasture management and rotational grazing. Regular deworming is also an essential part of horse and foal health care programs.

Can parasites in horses be transmitted to humans?

While it is uncommon, certain equine parasites can be transmitted to humans, mainly through contact with infected manure. However, proper hygiene such as washing hands after handling horses or manure can help reduce the risk of transmission.

What are some effective treatments for horse parasites?

Effective treatments for horse parasites generally involve the use of anthelmintic medications, also known as dewormers. The appropriate deworming protocol for each horse will depend on factors such as their age, environment, and exposure to parasites. It is essential to consult with a veterinarian to develop an individualized deworming program tailored to the specific needs of your horse.

Last Updated on August 23, 2023 by Nate Dewsbury

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