Horses are susceptible to many common illnesses and injuries that can impact their well being, performance, and longevity. From gut issues to respiratory conditions, muscle disorders, hoof problems and more, equine health conditions must be properly managed to avoid long-term problems.

Understanding common horse diseases is fundamental for everyone involved in equine care, as early recognition of the symptoms of disease can lead to better outcomes.

This guide covers 30 of the most common horse diseases observed in North America, so horse owners and caretakers can familiarize themselves with their symptoms, causes, treatments, and preventative measures

Whether you own a single horse or manage an entire stable, this comprehensive guide will equip you with the knowledge to keep your equine companions healthy and thriving.

Gastrointestinal Conditions

Horses have a very large gastrointestinal tract that is prone to developing disease. Horses can suffer from infections, obstructions, ulcers, and other conditions, all resulting in a need for veterinary care.

Choke

Choke refers to obstruction of the esophagus by feed or an ingested object. [1] Horses experiencing choke cannot swallow, and any consumed feed or water comes back up the esophagus and out the nostrils or mouth. [1]

The most common cause of choke is poorly chewed feed. [1] Horses that eat rapidly or have dental issues that prevent them from chewing properly are more likely to experience choke. [1] Some horses may develop choke due to previous injury to the esophagus wall or tumors compressing the esophagus. [1]

Symptoms of choke include: [1]

  • Retching
  • Extending the head and neck
  • Coughing
  • Large amounts of feed material coming from the nose
  • Sweating
  • Restlessness

Veterinarians diagnose choke using a nasogastric tube, a tube which goes from the nostrils into the stomach. [1] As the tube is passed through the throat, it makes contact with the obstructing material, indicating where the obstruction is located. [1] In most cases, the veterinarian administers fluids into the esophagus to break down the obstructing material and resolve the blockage. [1] Medications may also be administered to relax the esophagus muscles.

Most horses make a full recovery from a choking episode. [1] However, some horses may develop aspiration pneumonia if feed material entered their lungs. [1] Horses that have choked previously have an increased risk of future choking episodes. [1]

Nasogastric intubation should only be performed by a veterinarian. There is no safe way to intubate a horse at home.

 

Colic

Colic is not a specific disease or condition, it simply refers to pain in the abdomen. [1] Pain in the gastrointestinal tract causes most colic cases in horses, however pain in any abdominal organ has the potential to cause colic symptoms. [1]

Possible causes of colic include: [1]

  • Gastric ulcers
  • Inflammation in the intestines or colon
  • Parasitic infections of the gastrointestinal tract
  • Displacement or twisting of the intestine or colon
  • Obstruction of the colon or cecum by sand or undigested fibre
  • Gas distention of the colon or cecum
  • Abdominal tumors
  • Twisting of the uterus
  • Inflammation of the liver
  • Kidney stones

Symptoms of colic are highly variable, and depend on the severity of pain the horse is experiencing. [1] Possible signs of colic include: [1]

  • Reduced appetite
  • Lethargy
  • Reduced fecal production
  • Grinding teeth
  • Flehmen response
  • Laying down or rolling
  • Pawing
  • Biting, nipping, or kicking at the flanks and abdomen
  • Sweating
  • Inability to stand
  • Thrashing on the ground causing self-injury
  • Stretching out

The first goal for any veterinarian examining a case of colic is to determine whether the horse requires surgery or if the case is manageable with medication alone. [1] Receiving necessary surgical intervention soon after diagnosis improves the horse’s prognosis for survival. [1]

To determine the severity of the colic, diagnostics may include: [1]

  • Nasogastric intubation, passing a tube through a nostril into the stomach
  • Rectal palpation
  • Bloodwork
  • Abdominocentesis, taking a sample of fluid in the abdomen
  • Ultrasound
  • Endoscopy to evaluate the stomach
Nasogastric intubation should only be performed by a veterinarian. There is no safe way to intubate a horse at home.

Treatment and prognosis depend on the cause of colic. Some colic cases require surgery to remove dead or damaged abdominal tissues or place organs back in the correct positions. [1] Some colic cases respond to pain control, laxatives, and fluid therapy. [1] Horses that can be managed without surgery typically have a better prognosis. [1]

Dental Disease

Dental disease is very common in horses, particularly senior horses whose teeth are expiring. [2] Up to 50% of horses are reported to have dental disease. [1]

Horses’ teeth are naturally offset, as they have a wider upper jaw and narrow lower jaw. [2] This leads to irregular wear on the tooth surface, predisposing horses to dental abnormalities. [2]

Common dental issues in horses include: [2]

Horses with dental pain often have difficulty eating, drop feed (quidding), or eat slowly. [1] Some may have bad breath, weight loss, and reduced appetite. [1]

Diagnosing dental disease requires a thorough oral examination under sedation. [1] During these exams, veterinarians palpate the teeth, inspect them visually, and use picks to investigate pockets or spaces between teeth. [1]

Many equine dental problems are treatable with a routine dental float, however some conditions may require tooth extraction or surgical intervention. [1] It’s recommended for all horses to receive annual dental floats by a qualified practitioner as a preventative measure and to identify any developing problems early. [1]

Diarrhea

Diarrhea is an increase in the water content of feces. [1] Some cases of diarrhea are acute, lasting several days, and some are chronic, lasting more than 2 weeks. [1]

Equine diarrhea is associated with many conditions, including: [1]

Up to 50% of diarrhea cases in horses have no identifiable cause. [1]

Diagnosing the specific cause of diarrhea can help guide treatment and in some cases may point to a more severe underlying cause. [1]

Diagnostics may include: [1]

  • Bloodwork
  • Urinalysis
  • Abdominocentesis (taking a sample of fluid in the abdomen)
  • Ultrasound
  • Nasogastric intubation (passing a tube through a nostril into the stomach)
  • Rectal palpation
  • Fecal bacterial culture
  • Endoscopy to evaluate the stomach
  • Fecal sand sedimentation testing

Nasogastric intubation should only be performed by a veterinarian. There is no safe way to intubate a horse at home.

If required, treatment primarily involves supportive care to ensure that horses do not become dehydrated. Horses are not always able to replenish the large quantities of water and electrolytes lost during diarrhea without medical intervention. [1]

Treatment protocols may involve: [1]

  • Oral fluids provided through a nasogastric tube
  • Intravenous fluids
  • Antidiarrhea medications such as di-tri-octahedral smectite (Biosponge®)
  • Probiotics
  • Fecal microbial transplantation

The prognosis of diarrhea cases depends on the underlying cause. [1] Most horses make a full recovery from diarrhea episodes with appropriate management. [1]

Gastric Ulcers

Gastric ulcers are a defect in the lining of the stomach, revealing the underlying tissue. [1] Most horses develop gastric ulcers on the non-glandular portion of the stomach, which has little protection against the caustic properties of stomach acid. [1]

Gastric ulcers are extremely common in horses, with studies showing prevalence rates ranging between 11 – 100% depending on the group of horses examined. [1] Horses that are actively training, undergo prolonged periods of fasting daily, or who are fed a high grain, low roughage diet have a higher risk of ulcer development. [1]

Many horses with gastric ulcers show no obvious symptoms. [1] In horses that do show symptoms, symptoms can include: [1]

  • Reduced appetite
  • Poor performance
  • Weight loss
  • Behavioral changes
  • Mild colic

Veterinarians diagnose gastric ulcers by performing a gastroscopy, where a camera is passed into the stomach to examine the stomach lining. [1] Treatment involves medications like omeprazole, which reduce the production of stomach acid and allow the stomach lining to heal. [1]

Most horses recover from gastric ulcers, however ongoing management with antacid medications may be necessary. [1]

Internal Parasites

Internal parasites are very common in horses, with most horses carrying at least one type of parasite within their gastrointestinal tract. [3] Typically, horses acquire parasitic infections through ingesting parasite eggs from the environment. [3]

Common internal parasites in horses include: [3]

Most internal parasites do not cause significant disease in healthy adult horses unless they are present in a very large number or are damaging tissues. [3] Symptoms of parasitic disease can include: [3] Parasites are more dangerous in foals as they have not had a chance to develop any natural immunity.

  • Diarrhea
  • Colic
  • Weight loss
  • Swelling of the lower abdomen
  • Failure to shed foal coat
  • Stunted growth

Diagnosis of internal parasites involves a fecal egg count, which analyzes the number of parasite eggs present in the horse’s feces. [3] Veterinarians recommend these tests annually to monitor parasitic infections and ensure that horses with high parasite burdens are treated. [3]

Treatment involves an antiparasitic medication such as ivermectin or praziquantel. [3]

Ivermectin and praziquantel should only be administered based on veterinary recommendation and fecal egg count results, as there is increasing parasitic resistance to these medications.

 

Potomac Horse Fever

Potomac horse fever (PHF) is caused by an infection of Neorickettsia risticii bacteria. [1] N. risticii has a complex lifecycle, involving snails, flatworms, and aquatic insects like mayflies. [1] Drinking contaminated water or grazing on moist grass hosting aquatic insects are the most common routes of exposure for horses. [1]

After entering the large colon and cecum, N. risticii proliferates and causes inflammation and damage. [1]

Symptoms of PHF include: [1]

  • Fever
  • Reduced appetite
  • Lethargy
  • Colic
  • Diarrhea
  • Laminitis

Diagnosis of PHF involves a combination of bloodwork and diagnostic testing to identify the DNA of N. risticii. [1] Treatment for PHF is a specific antibiotic called oxytetracycline. [1] Anti-inflammatory medications and intravenous fluids are common supportive measures in the treatment protocol. [1]

Most horses with mild PHF symptoms make a full recovery within 3 – 5 days of treatment. [1] Horses with more severe symptoms or who develop laminitis have a poorer prognosis for recovery and survival. [1]

Respiratory Conditions

Horse lungs have a capacity of up to 55 litres, approximately nine times the capacity of human lungs. Large lung volume is necessary to provide adequate oxygen during exercise. Conditions affecting the lungs can significantly compromise a horse’s performance capacity and future potential.

Asthma

Equine asthma is the new collective term covering two conditions: [4]

Horses with equine asthma have a strong allergic reaction to dusts or molds in their environment. [5] The allergic reaction results in airway narrowing and accumulation of mucus within the lungs, making breathing difficult. [5]

The equine asthma spectrum ranges from mild to severe, with symptoms such as: [5]

  • Coughing
  • Nasal discharge
  • Increased abdominal effort when breathing
  • A “heave line”; increased prominence of the abdominal muscles
  • Increased respiratory rate
  • Poor performance
  • Exercise intolerance

Veterinarians primarily diagnose equine asthma through a combination of endoscopy and bronchoalveolar lavage, a diagnostic test where the veterinarian introduces saline into the lungs, extracts it, then evaluates the types of cells found in the sample. [4]

Treatment involves a combination of bronchodilators, to open the airways, and corticosteroids, to reduce inflammation. [5] Management changes are also necessary to reduce the horse’s exposure to the molds and dust that trigger the allergic response. [5]

Changes may include: [5]

  • Increasing turnout
  • Soaking or wetting hay and bucket meals
  • Using hay alternatives such as forage cubes
  • Using alternative, lower-dust bedding such as shavings or paper pellets
  • Optimize ventilation, even in winter
  • Remove horses from the barn when sweeping or cleaning

Equine asthma is a lifelong disease, however many horses’ symptoms can be managed with appropriate lifestyle changes and medications as necessary. [5]

Exercise-induced Pulmonary Hemorrhage

Exercise-induced pulmonary hemorrhage (EIPH) describes bleeding from the lungs and airways during strenuous exercise. [5] This condition is most common in racehorses and eventing horses. [5]

The exact cause of EIPH is unknown, but research suggests that increased heart rate and blood pressure during exercise may damage the fragile capillaries within the lungs, resulting in bleeding. [1] Typically the only symptom of EIPH is a mild nosebleed after performance. [1] “Bleeders” typically have a history of slowing down toward the end of a race or barrel run.

Endoscopy (passing a camera into the lungs) after exercise is the most common method for diagnosing EIPH. [1] If the veterinarian identifies blood in the lungs, then the diagnosis is confirmed.

There are currently no known treatments for EIPH. [1] However, some performance horses respond to administration of furosemide 4 hours prior to exercise. [1] Furosemide is a diuretic which encourages urine production, thus reducing blood volume and lowering blood pressure. [1] Most horses can continue their performance careers with an appropriate furosemide treatment plan. [1]

Influenza

Equine influenza is a respiratory virus closely related to the influenza viruses found in other species. [1] Horses exposed to large groups of unfamiliar horses, such as those going to shows or races, are more likely to become infected. [1] Young horses are also particularly susceptible to the virus. [1]

Symptoms of influenza infection include: [1]

  • Fever
  • Lethargy
  • Reduced appetite
  • Coughing
  • Nasal discharge
  • Eye discharge

Most veterinarians make a diagnosis of influenza based on the symptoms presented and a history of exposure to other horses. [1] To confirm the diagnosis, nasal swab tests to identify the virus’ genetic code or the virus itself are available. [1]

Most horses recover from influenza in 1 – 3 weeks with supportive care and stall rest. [1] Some horses may take up to three months to return to full athletic performance. [1] Affected horses that are actively shedding the virus should be quarantined away from other horses to prevent spread of the disease. [1]

A vaccine is available as a preventative measure for horses frequently exposed to larger groups of horses. [1]

Rhinopneumonitis Virus

Rhinopneumonitis virus, or equine herpesvirus, circulates in all equine populations. [5]

Carrier horses harbor the virus within their respiratory tract and shed the virus in their nasal secretions during periods of stress. [1] Horses contacting these secretions may develop rhinopneumonitis, an upper respiratory infection characterized by cough, nasal discharge, and fever. [1]

Veterinarians typically diagnose rhinopneumonitis based on the horse’s symptoms alone. To confirm a diagnosis of herpesvirus, nasal swabs or blood tests which look for the virus’ genetic code are necessary. [1]

There is no definitive treatment for herpesvirus, meaning horses must recover from the infection on their own. [1] Affected horses should have 2 – 4 weeks off exercise (other than turnout) and training to allow their airways to recover fully. [1]

Quarantine of these horses is also prudent as they can continue to shed the virus for up to 2 weeks after symptoms resolve. [1]

Vaccines that reduce the risk of developing symptoms from herpesvirus infection are available. [1] Most veterinarians recommend vaccinating horses who are frequently exposed to large horse groups (such as horse shows or events) every 3 – 6 months. [1]

Shipping Fever

Shipping fever, also called pleuropneumonia, is a respiratory infection commonly associated with long periods of transport. [1] During long-haul transport, horses often have their heads tied up, which prevents them from lowering their head to clear contaminants from their airways. [5] This increases the risk of inhaled bacteria colonizing the lungs and causing an infection. [5]

Pleuropneumonia causes symptoms such as: [1]

  • Fever
  • Rapid breathing
  • Nasal discharge
  • Coughing
  • Exercise intolerance

Veterinarians can diagnose pleuropneumonia on ultrasound, which shows fluid within the chest and surrounding the lungs. [1] Treatment involves antibiotics that target the bacteria causing the infection, and anti-inflammatories. [5]

The prognosis of pleuropneumonia is highly variable, and depends on the severity of infection, time between infection and treatment, and the horse’s response to treatment. [1]

Strangles

Strangles is infection with Streptococcus equi, a highly infectious bacterium that affects the respiratory tract. [1] Horses develop strangles after inhaling or ingesting the bacteria from their environment, or after contact with an infected horse. [1] Young horses are most susceptible to infection. [1]

Symptoms of strangles include: [1]

  • Fever
  • Lethargy
  • Swelling of the lymph nodes
  • Rupture of lymph nodes with exuding pus
  • Nasal discharge
  • Difficulty breathing

Veterinarians take nasal swabs or samples of the pus material to submit for laboratory evaluation. [1] These tests either identify S. equi itself, or the bacteria’s DNA. [1]

Quarantine of all horses affected by strangles is critical to prevent further spread of disease. [1] Treatment typically involves anti-inflammatories to reduce fever and hot packing of abscesses to encourage drainage. [1] Antibiotics are not used unless the infection progresses beyond the lymph nodes and the horse is seriously ill.

During the treatment process, several rounds of diagnostic testing are necessary to ensure that the bacteria is fully cleared before the horse returns to the general population. [1] Typically horses are quarantined until they have a negative result on three separate diagnostic tests. [1] Most horses make a full recovery from strangles infection. [1]

There is a strangles vaccine available which reduces the severity of symptoms if a horse becomes infected. [1]

Endocrine Conditions

Endocrine conditions are disorders affecting the horse’s hormones and how they function. There are two main endocrine conditions in horses: equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID).

Equine Metabolic Syndrome

Equine metabolic syndrome (EMS) is an endocrine disorder resulting in insulin resistance, a scenario where there is ineffective transport of sugar from the bloodstream into cells with insulin receptors. [1] Breeds predisposed to EMS include: [1]

Many horses with EMS are obese, and are often referred to as “easy keepers“. [1] Affected horses are also prone to developing chronic laminitis that may flare-up when horses ingest a diet high in sugar and starch (hydrolyzable carbohydrates). [1]

Diagnosis of EMS involves blood testing for insulin levels, as horses with EMS have high blood insulin as a characteristic finding. [1] Veterinarians may also test the horse’s response to sugar in their diet, to evaluate whether their body responds to increased blood sugar appropriately. [1]

Treatment of EMS involves diet and lifestyle changes. EMS horses should have no higher than 10% hydrolyzable carbohydrate. Pasture is usually avoided since HC levels vary widely over the course of a day.

Increased exercise is also recommended for weight loss in obese horses. [1] Some horses may also need high doses of thyroid hormone to encourage weight loss as part of their treatment plan. [1]

EMS is usually manageable with an appropriate diet and increased exercise. [1] Animals with refractory high insulin may respond to medications like metformin or canagliflozin. [6] However, some horses may have a poorer prognosis if they have significant damage to their hoof structure due to chronic laminitis. [1]

Pituitary Pars Intermedia Dysfunction

Pituitary pars intermedia dysfunction (PPID), formerly known as equine Cushing’s disease, is a progressive condition resulting from changes in the pituitary gland. This gland is located in the brain and produces hormones that control other internal organs within the body. [1]

PPID is most common in horses over 15 years of age, with between 15 – 30% of aged horses having the disorder. [1]

Symptoms of PPID include: [1]

Veterinarians diagnose PPID through blood tests for ACTH, one of the major hormones produced by the pituitary gland. [1] Treatment involves daily administration of the medication pergolide (Prascend®), which counteracts the changes in the pituitary gland and restores normal hormone function. [1]

PPID can also be accompanied by insulin resistance. Horses with PPID and concurrent insulin resistance should be fed a diet low in hydrolyzable carbohydrates.

Since PPID is a lifelong disease, ongoing monitoring is necessary to prevent symptom relapse. [1] Many horses with PPID can have comfortable lives and even performance careers with appropriate management. [1]

Musculoskeletal Conditions

Musculoskeletal conditions are common in horses, and can compromise their ability to perform in equestrian sports. Regular evaluation by a veterinarian can help identify certain conditions, such as arthritis or back pain, early.

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Arthritis

Arthritis refers to inflammation in a joint, and is a common cause of lameness in horses. [7] Any joint in the horse’s body can develop arthritis. There are many possible causes of arthritis, including injuries in or around the joint, excessive use of a joint, and aging. [7]

This can result in loss of normal joint cartilage, a flexible tissue that provides a smooth surface for joint motion. [7] Without joint cartilage, the bones composing the joint grind against each other, causing pain and lameness. [7] Horses with arthritis may resist flexion of the affected joint or seem stiff or sore. [7]

When evaluating a horse that may have arthritis, veterinarians use a lameness examination to determine which joints are most likely affected. [7] From there, they can X-ray the joints to identify bony changes characteristic of arthritis, and confirm the diagnosis. [7]

Veterinarians consider arthritis an irreversible disease, however treatment strategies can slow the progression of arthritis and make horses more comfortable. [7] Many treatment options are available for arthritis, including: [7]

With an appropriate management plan, many horses with arthritis continue performance careers successfully. [7]

Back Pain

Back pain is a common cause of lameness and poor performance in horses. [7] Causes of back pain include: [7]

Symptoms of back pain vary between horses, and can include: [7]

  • Poor performance
  • Resistance to bending one direction
  • Bucking or kicking out
  • Crossfiring or switching leads in the canter
  • “Bunny hopping” in the canter
  • Difficulty with collection
  • Refusing jumps

A thorough lameness examination is necessary to determine the cause of back pain. [7] The examination may include palpation of the back, flexing the neck and spine, X-rays, or ultrasound. [7]

Treatment depends on the cause of back pain, and ranges from simply rest and anti-inflammatories to surgical intervention. [7]

Traumatic Injuries

Traumatic musculoskeletal injuries are very common in horses, with one study showing that 40% of horse owners reported their horse sustained an injury in the previous year. [7] Traumatic injuries may include: [7]

In cases of severe injury, veterinarians quickly assess the horse before providing sedation to keep the horse calm for further evaluation. [7] Pain control medications, such as anti-inflammatories or opioids, can also help facilitate evaluation by reducing the horse’s pain levels. [7] If the horse lost a large amount of blood a blood transfusion may be required. [7]

After stabilizing the horse, the veterinarian evaluates the injury to assess the extent of damage. [7]

Diagnostics may include: [7]

  • X-rays
  • Ultrasound
  • Evaluating joint integrity through fluid analysis or joint tapping
  • Probing a wound using a sterile tool

The immediate treatment plan depends on the type of injury. [7] Some injuries, such as bone fractures or tendon ruptures, may require surgery to heal completely. [7] Other injuries, such as those affecting a joint, may require hospitalization for intensive treatment. [7]

For these types of injuries, the veterinarian evaluating the horse will place a cast or bandage to stabilize the leg for transport. [7] Upon arrival at the hospital, further diagnostic tests may be necessary to determine a treatment plan. These injuries have a variable prognosis depending on the horse’s response to treatment and the location and severity of the injury. [7]

For minor wounds, treatment can involve a combination of flushing the wound, suturing, antibiotics, bandaging, and anti-inflammatories. [7] Most horses recovery from minor wounds uneventfully, however they may have permanent scarring. [7]

Skin Conditions

The skin is a major defense system, protecting the horse from infectious agents they encounter in their environment. Damage to the skin is a potential route for infection to enter the horse’s body, making routine examination of their skin an important aspect of maintaining their overall health.

Pigeon Fever

Pigeon fever is a bacterial infection caused by Corynebacterium pseudotuberculosis. [8] This condition is most common in the western United States. [8] Horses develop an infection when biting flies deposit the bacteria into a bite wound. [8]

The bite wound forms an abscess under the skin surface that may rupture and drain. [8] Abscesses are most common on the shoulder, neck, back, and chest. [8] Many horses also have skin irritation and swelling in the abdomen. [8]

Veterinarians can diagnose pigeon fever by examining a smear of the abscess material under a microscope or submitting it for bacterial culture. [8] Treatment involves draining the abscesses and cleaning the area with an antiseptic. [8] Most horses do not develop pigeon fever again after their initial infection resolves. [8]

Scratches

Scratches refers to inflammation and irritation of the skin on the pasterns. [8] Horses develop crusty, scabby skin that may be itchy or painful. [8] The most common location for scratches is the back of the pastern, particularly on legs with white markings. [8]

There are many potential causes of scratches, including: [8]

  • Bacterial infections
  • Fungal infections
  • Mange
  • Contact with irritating substances
  • Photosensitization
  • Autoimmune disorders

Diagnosing the cause of scratches requires a thorough investigation. Diagnostics may include: [8]

  • Skin scrapings
  • Hair plucking
  • Bacterial culture
  • Fungal culture
  • Skin biopsy
  • Bloodwork

The treatment for scratches depends on the underlying cause. [8] Horses may require routine cleaning of the area, antibiotics, steroids, or lifestyle changes to resolve the condition. [8] Many horses with scratches experience frequent relapses, requiring ongoing treatment and management by their owners. [8]

Skin Cancer

Skin cancers are common in horses, particularly sarcoids, squamous cell carcinomas, and melanomas. [8] Some cancers develop in sites frequently exposed to UV light or in areas of previous skin injury. [8] Others occur due to genetic predisposition, such as melanomas in grey horses. [8]

Skin cancers can develop anywhere on the body. [8] Common locations include: [8]

  • Around the lips
  • Around the eyes and on the eyelids
  • Legs
  • Under the tail

Most skin cancers start as a small mass that grows over time. [8] Some may develop a cauliflower-like appearance as they grow. [8] Often the skin overlying the tumor is very fragile, and bleeds easily when the tumor is bumped or rubbed against objects. [8]

A skin biopsy is necessary to confirm the type of cancer present, and to determine whether it is malignant (aggressive). [8] Some types of tumors have characteristic features that veterinarians may use to make a tentative diagnosis while waiting for biopsy results. [8]

Treatment options for skin cancers include: [8]

  • Surgical removal
  • Cryotherapy
  • Laser therapy
  • Chemotherapy
  • Immunotherapy

A combination of these treatment modalities may be necessary to completely remove a tumor. [8]

The prognosis depends on the type of tumor present, the degree of malignancy, and whether there are metastases elsewhere in the horse’s body. [8] Aggressive tumors typically have a poor prognosis, with many owners electing for humane euthanasia. [8]

Rain Rot

Rain rot is a skin infection with the bacterium Dermatophilus congolensis. [8] The bacterium only causes infection if there is damage to the skin’s protective layer from injuries, biting insects, or excessive moisture. [8] However, Rain Rot may occur in only one individual in a group if that horse has a compromised immune response.

Rain rot causes characteristic “paintbrush lesions“, which are scabs containing a tuft of hair similar to a paintbrush. [8] Underneath the scabs, horses often have red skin or a small wound producing pus. [8] Paintbrush lesions are most common over the rump, back, and neck. [8]

Diagnosis of D. congolensis involves examining one of the hair tufts under a microscope. [8] The bacteria have a characteristic railroad track appearance that veterinarians can recognize. [8] Some cases may require bacterial culture or a skin biopsy to diagnose. [8]

Most cases of rain rot resolve within four weeks if the horse is kept dry. [8] This may involve management changes such as stabling or blanketing to keep moisture from contacting the skin. [8] Other treatments include topical antiseptic or antibiotic solutions applied to the crust locations or used as a whole-body shampoo. [8]

Hoof Conditions

“No hoof, no horse” is a common phrase around horse facilities, and reflects the significance of the hoof as the horse’s major weight bearing structure. Hoof conditions are a common cause of lameness in horses, and may result in poor performance, lost performance days, and even early retirement.

Abscesses

A hoof abscess is an accumulation of pus within the hoof capsule due to a bacterial infection. [7] Abscesses usually form after bacteria enters a crack or fissure in the hoof wall and begin proliferating. [7] Over time, this produces a pocket of pus that can cause severe pain due to compression of sensitive hoof tissue. [7]

The most common sign of a hoof abscess is sudden onset severe lameness. [7] However, many serious conditions can cause similar symptoms, so evaluation by a veterinarian is always necessary. [7]

Veterinarians diagnose hoof abscesses by using hoof testers to identify the location of the abscess. [7] X-rays can also identify the location of a hoof abscess by showing a tract of air within the hoof. [7]

Treatment focuses on draining the abscess to relieve pain. [7] A veterinarian or qualified farrier can pare away the hoof wall to expose the abscess. [7] For abscesses deep within the foot, specialized poultices and soaking the foot can encourage the abscess to move closer to the surface where it is accessible for drainage. [7]

Once the abscess drains, a bandage or hoof boot with an antiseptic product helps prevent re-infection by keeping the drainage site clean. [7] Typically the lameness associated with a hoof abscess resolves within 12 – 24 hours after drainage begins, and the drainage site heals over several weeks as the hoof regrows. [7]

Laminitis

Laminitis refers to inflammation and separation of the lamellae, fine interdigitating tissues that support the coffin bone within the horse’s hoof. [7] The lamellae contain numerous nerves and blood vessels, making the separation of these tissues extremely painful. [7]

laminitis vs. healthy hoof | Mad Barn USAIllustration:

Causes of laminitis include: [7]

  • Endocrine disease, such as pituitary pars intermedia dysfunction or metabolic syndrome
  • Sepsis, a bacterial infection of the bloodstream
  • Supporting limb laminitis, caused by excessive weight bearing due to lameness on an opposing limb
  • Toxins such as black walnut

Horses can have either acute (sudden onset) or chronic (prolonged) laminitis. [7]

Symptoms of acute laminitis include: [7]

  • Severe lameness with stiff limb movement
  • Increased temperature in the hooves
  • Increased digital pulse (pulse in the lower limb)
  • “Sawhorse stance” where the horse places their front limbs forwards and rocks backward onto their hindquarters

Horses with chronic laminitis can show similar symptoms, particularly during a flare-up of laminitis. [7] Additional signs of chronic laminitis include a convex shape to the front of the hoof capsule, with the hoof rings being wider at the heel and narrow at the toe. [7]

Veterinarians often suspect laminitis based on the horse’s symptoms alone. [7] To confirm the diagnosis, the veterinarian takes X-rays of the hooves to identify sinking or widening in the hoof-lamellar zone. [7] Additional diagnostics, including bloodwork, may also be necessary if the underlying cause of laminitis is unknown. [7]

Treatment for laminitis depends on the type of laminitis and whether there is active separation of the lamellae occurring. [7]

Treatment may include: [7]

The prognosis for laminitis varies widely, depending on the underlying cause and degree of separation. [7] Some horses successfully return to performance careers after developing laminitis with appropriate treatment and management. [7]

Navicular Syndrome

Navicular syndrome, also known as podotrochlear syndrome, is a common cause of front limb lameness in horses. [7] Studies suggest that navicular syndrome causes one-third of all chronic lamenesses in the front limbs in horses. [7] Quarter horses, Thoroughbreds, and warmbloods have a higher risk of developing this syndrome. [7]

Navicular syndrome is not one specific condition or disease, it refers to any injury causing pain in the podotrochlear apparatus. [7] This apparatus includes all of the ligaments, soft tissues, and bones in and around the navicular bone. [7]

These structures may become damaged due to abnormal forces on the apparatus from poor hoof trimming, obesity, conformational abnormalities, or excessive work on hard surfaces. [7]

Symptoms of navicular syndrome include: [7]

  • Poor performance
  • Stiffness and shortening of the stride
  • Unwillingness to turn
  • Increased lameness when working on hard surfaces

Since there are numerous potential causes of navicular syndrome, achieving a precise diagnosis can be challenging. [7] However, having a precise diagnosis can improve outcomes by ensuring the treatment plan targets the correct structures to relieve pain. [7]

Veterinarians usually suspect navicular syndrome based on their lameness examination. [7] From there, they may recommend additional diagnostics such as X-rays, MRI, ultrasound, or bone scans to identify the painful structure. [7]

Treatment for navicular syndrome primarily depends on the affected structure. Treatment plans may include: [7]

  • Corrective trimming and shoeing
  • Pain control medications
  • Anti-inflammatory injections of the navicular bursa or coffin joint
  • Bisphosphonates, such as tiludronate or clodronate
  • Surgical intervention

Navicular syndrome is a lifelong condition, with symptoms typically worsening over time despite treatment. [7] Many horses eventually retire from performance careers due to unsoundness. [7]

Thrush

Thrush is a bacterial infection of the base and sides of the frog. [7] Thrush is most common in horses standing in wet or unhygienic conditions which allows bacteria to penetrate the frog tissue and cause damage. [7]

Signs of thrush include: [7]

  • Black exudate around the frog
  • Foul odor
  • Loss of frog tissue
  • Lameness in severe cases

Evaluation of the hoof allows veterinarians to diagnose thrush and recommend a treatment plan. [7] Treatment typically involves a combination of farriery changes, to encourage better clearing of debris from around the frog, removal of dead, infected tissue, and topical antiseptics such as iodine, copper sulfate, or chlorhexidine. [7]

Horses that are prone to thrush require dry bedding or footing, frequent and thorough hoof cleaning, and regularly scheduled farriery appointments. [7]

Eye Conditions

Horses have some of the largest eyes of any land mammal, an adaptation that allows them to easily identify predators in their environment. Conditions affecting the eyes may cause blindness, making prompt recognition of ocular diseases critical.

horse-eye-anatomy | Mad Barn USAIllustration:

 

Any obvious or suspected eye or vision disorder is considered a medical emergency. Urgent veterinary intervention provides the best chance of preserving vision.

 

Moon Blindness

Moon blindness, or equine recurrent uveitis (ERU), is an autoimmune disorder that results in destruction of tissues within the eye. [9] Studies show that ERU is the most common cause of blindness in horses. [9]

ERU is a multifactorial disease, meaning that many risk factors may contribute to the development of the condition. [9] Currently identified risk factors include: [10]

  • Bacterial infections, particularly Leptospira infection
  • Viral infections, including equine herpesvirus
  • Age
  • Genetic predisposition, particularly in leopard spotted breeds

The symptoms of ERU often wax and wane during the horse’s lifetime. [9] Symptoms during flare-ups may include: [9]

  • Squinting
  • Ocular discharge
  • Cloudy appearance to the eye
  • Swelling around the eye and eyelids
  • Constricted pupil
  • Excessive tearing

A thorough ocular examination is necessary to diagnose equine recurrent uveitis and distinguish it from other eye disorders. [9] This may include evaluation with an ophthalmoscope, application of fluorescein dye, measuring ocular pressure, and ultrasound of the eyeball. [9] Examination with an ophthalmoscope is necessary if structures deeper than the surface may be involved.

ERU is a lifelong disorder with no known cure. Treatment focuses on preventing flare-ups and managing symptoms if they do occur. [9] Most horses will eventually become blind from ERU. [9]

Traumatic Eye Injuries

Horses’ eyes protrude from their skull, putting them at risk of traumatic injuries to the eye surface. [9] Examples of eye injuries include: [9]

  • Foreign materials such as sticks, foxtails, or other items scratching or penetrating the eye
  • Lacerations of the eye surface from rubbing the eye on objects
  • Whiplash injury from running through low branches
  • Blunt force trauma, such as kicks from other horses

Horses with damage to the eye surface often show symptoms such as: [9]

  • Squinting
  • Ocular discharge
  • Changes in the opacity of the eye
  • Swelling around the eye
  • Holding the eye closed

Veterinarians evaluate the eye using fluorescein dye to identify any foreign objects or tears in the eye surface. [9] Fluorescein stains any defects in the normally smooth eye surface, highlighting small injuries. [9] Other diagnostics such as ultrasound or using special magnifying lenses (biomicroscopy) may be necessary in some cases. [9]

Treatment involves removing any foreign objects present, then encouraging healing of the eye surface. [9] Veterinarians usually recommend topical medications applied directly to the eye, allowing high concentrations of the medication at the injury site. [9]

Common medications include antibiotics, atropine to encourage pupil dilation, anti-inflammatories, and blood serum to provide healing factors. [9]

Most traumatic injuries to the eye have a good prognosis. [9] However, severe injuries may not be salvageable and require surgical removal of the eye (enucleation) to improve the horse’s comfort. [9] It’s important to note horses are able to adapt to loss of an eye and live full, comfortable lives after enucleation. Some even return to athletic careers after loss of an eye.

Neurologic Conditions

Neurologic conditions are diseases that affect the nervous system, including the brain and spinal cord. These conditions can make horses behave erratically, lose coordination, and even fall, making them a safety risk for handlers. Some neurologic diseases are also a potential human health risk.

Equine Protozoal Myeloencephalitis

Equine protozoal myeloencephalitis (EPM) is a parasitic infection caused by the protozoan Sarcocystis neurona. [5]

This parasite produces an infective form in its definitive host, the opossum, which is shed in the opossum’s feces. [5] Horses ingest the infectious agent in water or feed contaminated by opossum feces. [5] After infecting the horse, the parasite causes widespread inflammation in the brain and spinal cord. [5]

Symptoms of EPM include: [5]

  • Uncoordinated movement (ataxia)
  • Asymmetrical muscle atrophy
  • Head tilt
  • Difficulty chewing

Confirming a diagnosis of EPM is difficult, as the parasite only exists within the central nervous system during an infection. [5] Veterinarians typically rule out other causes of ataxia first using X-rays, neurologic examination, and viral testing. [5] Submitting a sample of cerebrospinal fluid, the fluid around the brain and spinal cord, is the gold standard for diagnosis of EPM. [5]

There are several antiparasitic medications available for treating EPM, including ponazuril. [5] Treatment typically takes around 28 days. [5] Some horses relapse after the initial treatment regimen and require a longer treatment period. [5]

The overall prognosis for EPM is fair, with treatment reducing the severity of symptoms in 60 – 75% of horses. [5]

Routine Vaccinations

Veterinarians recommend five core vaccinations for all horses in North America, to protect them against life-threatening diseases. Veterinary consensus groups choose the core vaccines based on the severity of the infection, risk to human health, and the ease of spread between affected horses. [11]

The core vaccines are: [11]

All of these diseases affect the central nervous system, causing symptoms such as: [1]

  • Uncoordinated movement (ataxia)
  • Weakness
  • Fever
  • Head pressing
  • Seizures
  • Severe lethargy
  • Death

Thanks to ongoing vaccination programs, these diseases are now uncommon in North American horses. Horse owners should work with their veterinarian to establish a suitable vaccination program for their herd.

Horse Health: A Matter of Management

The bond between horses and their caretakers is one of a kind. Horse owners the world over have to make informed decisions every day about their horses’ diets, exercise, training, socialization, and health care.

By familiarizing yourself with the most common equine health concerns, you can take proactive steps to prevent them and know when to call a veterinarian for help. Staying up to date with routine preventive care like dental floatation, farriery, vaccines, fecal egg counts, and regular check ups provide the best conditions for your equids to live a long, happy life.

Another cornerstone of preventive health care is balanced and robust nutrition. Whatever your horse’s age, discipline, or health status, maximizing forage intake and properly balancing their diet goes a long way to set them up for continued success.

Not sure whether your horse’s diet is meeting all of their needs? Submit a free diet evaluation today and have one of our qualified equine nutritionists take a look at your feed regimen.

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References

  1. Lavoie. J.-P., Ed., Blackwell’s Five-Minute Veterinary Consult. Equine. Third edition. Wiley-Blackwell, Hoboken, NJ. 2019.
  2. Pearce. C., Recent Developments in Equine Dentistry. New Zealand Veterinary Journal. Taylor & Francis. 2020. View Summary
  3. Internal Parasite Control Guidelines. American Association of Equine Practitioners. 2024.
  4. Couetil. L. et al., Equine Asthma: Current Understanding and Future Directions. Frontiers in Veterinary Science. 2020. View Summary
  5. Reed. S. M. et al., Equine Internal Medicine. 3rd ed. Saunders Elsevier, St. Louis, Mo. 2010.
  6. Kellon. E. and Gustafson. K., Use of the SGLT2 Inhibitor Canagliflozin for Control of Refractory Equine Hyperinsulinemia and Laminitis. Open Veterinary Journal. 2022.
  7. Baxter. G. M., Ed., Adams and Stashak’s Lameness in Horses. Seventh edition. Wiley-Blackwell, Hoboken, NJ. 2020.
  8. Scott. D. W. and Miller. W. H., Equine Dermatology. W.B. Saunders, Saint Louis. 2003.
  9. Gilger. B. C., Ed., Equine Ophthalmology. Third edition. Wiley Blackwell, Ames, Iowa. 2017.
  10. Kingsley. N. B. et al., A Review of Investigated Risk Factors for Developing Equine Recurrent Uveitis. Veterinary Ophthalmology. 2023. View Summary
  11. Vaccinations for Adult Horses. American Association of Equine Practitioners. 2023.