Parasites in horses: detection, treatment and prevention

Parasites are a common but often underestimated health issue in horses. They can affect a horse's external appearance as well as its internal system – and, if left untreated, can lead to serious health problems. In this comprehensive guide, we explain which parasites are common in horses, how to identify, treat, and prevent them – based on current veterinary knowledge and practical experience.

What are parasites in horses – and what types are there?

Parasites are organisms that live at the expense of their host. In horses, a distinction is made between ectoparasites (external parasites, e.g., mites or lice) and endoparasites (internal parasites, e.g., roundworms or liver flukes). Both groups can pose a health risk, especially in cases of weakened immune systems, poor housing conditions, or inadequate prophylaxis.

The most important parasite species in horses:

Parasite species	type	Common representatives	Main seat in the horse
Ectoparasites	External parasites	Mites, lice, fleas, lice	Skin, fur, mane
Endoparasites	Internal parasites	Roundworms, strongyles, liver flukes, lungworms	Intestine, liver, lungs

Parasites aren't just annoying. Chronic infestation weakens the immune system and can lead to inflammation, growth disorders (especially in foals), or colic . Therefore, it's crucial to know the typical identifying signs.

How do you recognize parasites in horses?

Parasite infestation manifests itself differently depending on the species. However, the first signs are often general: unexplained weight loss, dull fur, or changes in behavior . Here's an overview of typical symptoms:

Common symptoms of parasite infestation:

• Weight loss despite normal feeding
• Itching or rubbing of the tail and mane
• Hair loss, skin redness, crusts
• Dull, shaggy fur
• Diarrhea, changing stool consistency
• Bloated abdomen, especially in foals
• Breathing difficulties (especially with lungworms)
• Colic-like symptoms

If you notice such signs, don't hesitate: A stool analysis or skin examination by a veterinarian will provide clarity. Many symptoms can also indicate other diseases.

Which ectoparasites can infect horses?

Ectoparasites infest the skin's surface and feed on skin particles, blood, or sebum. They primarily cause skin problems such as mange, eczema, or hair loss.

Mites: Chorioptes and Sarcoptes

• Chorioptes (burrowing mites): Common in horses with feathers. Typical symptoms: severe itching, crusting, especially on the fetlocks.
• Sarcoptes: They cause so-called sarcoptic mange. Rare, but highly infectious. Symptoms include widespread skin reddening, crusting, and hair loss.

Lice and biting lice

• Lice are small insects that feed on skin flakes. They are recognizable by their nest-like appearance, itching, and dull fur. They are particularly common in the winter months.
• lice Similar to biting lice, they cause itching, chafing, and skin irritation. Severely infested animals are restless and exhibit reduced performance.

Fleas and grass mites

• Fleas are rare in horses, but are more likely to be transmitted from other animals.
• Grass mites (autumn grass mites) usually appear between July and September, especially on damp pastures. Itching and bumps on the mouth and legs are typical symptoms.

Skin changes caused by parasites

Numerous parasites cause secondary skin changes : weeping eczema, crusts, scales, or even open wounds. Consistent skin care is just as important as treating the underlying cause.

Which endoparasites occur in horses?

Endoparasites live inside the horse's body – usually in the digestive tract – and from there damage organs, nutrient absorption, and the immune system. Targeted parasite management is particularly important here.

Roundworms (Parascaris equorum)

Roundworms are particularly common in foals and young horses. They can grow up to 40 cm long. Symptoms:

• Cough, dull appearance
• Bloated stomach
• Massive colonization can cause colic or intestinal obstruction

Strongyles (large and small)

Strongyles are among the most dangerous endoparasites in horses. They damage intestinal walls and blood vessels.

• Small strongyles (Cyathostominae): Often remain asymptomatic until mass reproduction, followed by diarrhea and weight loss.
• Large strongyles (Strongylus vulgaris): Migration through blood vessels to the intestine – vascular injuries, risk of colic.

Lungworms (Dictyocaulus arnfieldi)

Particularly relevant when grazing donkeys, as donkeys are long-lived carriers.

• Symptoms: Cough, shortness of breath, reduced exercise tolerance
• Diagnosis usually via special stool examination or bronchial secretion

Liver fluke (Fasciola hepatica)

Rather rare, but with serious effects, especially in humid regions with snails as intermediate hosts.

• Symptoms: Weakness, yellowing (jaundice), liver swelling
• Treatment requires targeted deworming with liver-active medications

What illnesses can parasites cause?

A parasitic infestation can not only cause local problems, but can also trigger serious systemic diseases – a fact that is often underestimated.

Colic as a result of parasites

An acute or chronic parasite infestation can irritate or even block the intestinal mucosa – colic is often the first serious warning sign.

Typical course:

• Restlessness, tossing and turning, sweating
• Without treatment, intestinal obstructions may occur

COB (Chronic Obstructive Bronchitis)

Often associated with environmental influences, but can also be triggered parasitically (e.g. by lungworms).

• Symptoms: chronic cough, reduced performance, shortness of breath
• Diagnosis by bronchoscopy or laboratory examination

When and how do you deworm horses correctly?

Deworming is the central measure for combating endoparasites . The strategy has changed significantly in recent years, moving away from fixed "worming regimens" toward selective, targeted treatment.

Selective deworming

First, a stool sample is taken to determine whether and to what extent an infestation is present. Deworming is only initiated if the result is positive, thus reducing resistance.

Worming treatment: application, remedies and dosage

• Worming treatments are administered orally (paste, gel)
• Popular active ingredients: Ivermectin, Moxidectin, Fenbendazole, Pyrantel
• Type and dosage depend on weight, parasite type and living situation

Important: Don't deworm on suspicion. Too frequent or non-specific deworming promotes resistance.

How can parasites in horses be effectively prevented?

Prevention does not begin with the next worming treatment, but in the stable, on the pasture and in care.

Stable and pasture hygiene

• Daily mucking out of stables and pastures
• Changing pastures (rotational grazing)
• Avoiding excessively dense livestock stocking
• Do not spread manure on horse pastures

Does a good immune system strengthen the defense against parasites?

Yes. Horses with stable intestinal flora and a well-nourished body are less susceptible. A balanced feed ration, minerals, exercise, and stress reduction have been proven to strengthen the immune system.

Are there alternative treatments for parasites?

In addition to conventional deworming medications, many horse owners also use naturopathic or homeopathic approaches – for example, to support liver function after heavy medication exposure.

Homeopathic treatment

• Use for minor complaints or for convalescence
• Typical remedies: Nux vomica, Sulfur, Carduus marianus (milk thistle)

Herbal preparations

• Garlic, wormwood or pumpkin seeds are traditionally used to ward off parasites – however, scientific evidence is limited
• Do not use as a replacement, but at best as an accompaniment

Important: Natural remedies cannot reliably combat parasite infestation. Purely alternative treatment should never be the sole option—especially in cases of severe infestation.

Detect parasites, minimize risks, act specifically

Parasites are unfortunately a part of everyday life on horses. However, with consistent monitoring, proper management, and thoughtful deworming, infections can be detected early and contained in the long term. Knowing the symptoms, conducting regular fecal screenings, and responding attentively to skin changes will protect your horse's health in the long term and prevent costly complications.

Frequently asked questions and answers

1. What parasites are there in horses?

There are various parasites that can be found in horses, including intestinal worms (such as roundworms and strongyles), skin parasites (such as mites and fleas), and ectoparasites (such as lice). Each of these parasites can cause different health problems, which is why regular monitoring and prevention are important.

2. How do I recognize symptoms of parasites in my horse?

Typical symptoms of parasites in horses include weight loss, poor coat condition, coughing (in the case of lungworms), diarrhea or colic, and skin changes (in the case of skin parasites). Immediate veterinary attention is recommended if any noticeable symptoms occur.

3. How does deworming work in horses?

Deworming is usually done with special worming treatments or oral dewormers. Deworming is recommended at least twice a year, depending on the horse's specific risks and living conditions. A fecal examination can help determine individual needs.

4. What can I do to prevent parasites in horses?

To prevent parasite infestation, you should conduct regular deworming, maintain stable and pasture hygiene, and ensure that your horse does not live in overcrowded pastures. A balanced diet can also strengthen the immune system and make your horse less susceptible.

5. What skin diseases can be caused by parasites in horses?

Skin parasites such as fleas and mites can cause various skin diseases in horses, such as mange (equine mange) or allergic reactions. Typical symptoms include itching , hair loss, and redness. If skin parasites are suspected, a veterinarian should be consulted.

6. What are the consequences of an untreated parasite infestation?

Untreated parasitic infestation can lead to serious health problems, including growth stunting in young horses, severe colic, anemia, or even life-threatening conditions. In the long term, this can severely impact the horse's overall quality of life. Therefore, early diagnosis and treatment are crucial.