Common Diseases of Horses

Icon of a book

Common Diseases

It is important to observe animals often to detect changes in their general condition and overall health. 

Many diseases can be transmitted from horse to horse by shared feed bunks, buckets or watering troughs. Vaccinations for common infectious diseases are inexpensive and effective and should be administered on a yearly basis. Your veterinarian can recommend vaccinations that are appropriate for your horse.

Vaccines are made from inactive forms of the organism that cause the disease. After a horse is vaccinated, its immune system will make antibodies to fight that disease. There can be different opinions on how often vaccinations should be given, how long they will remain effective and at what age they should begin.

The best time for annual vaccinations is in early spring before the insect season starts. Veterinarians should be consulted when establishing a regular schedule for vaccinations.

LINK: Check out this Vaccination Equi-Planner Healthcare Tool by Equine Guelph to help you generate a recommended vaccination schedule for your horse and region.

Remember a horse’s immune system takes a minimum of two weeks to make the antibodies needed, so vaccinations should be administered at least three to four weeks before potential exposure to diseases.

What does the Code of Practice for the Care and Handling of Equines say about signs of illness?

“The most common signs of illness include: 

  • Change in the horse’s behaviour (e.g., lethargic, depressed, anxious)
  • Reduced feed intake 
  • Change in water intake 
  • Change in consistency of manure
  • Unexplained change in weight (loss or gain)
  • Signs of pain or discomfort (e.g., reluctance to move, increased rate of respiration and sweating)
  • Signs of colic 
  • Lameness
  • Swelling
  • Discharge from the eyes, ears or nose
  • Coughing or difficulty breathing
  • Fever.

Take action immediately if any horse is injured or appears ill or distressed. If you are in doubt about the horse’s health or the most effective treatment, consult a veterinarian without delay.”

DO YOU KNOW enough about the importance of monitoring vital signs? If you think you need to find out more, refer back to the "Vital Signs of a Horse" topic covered in this module.

The following requirements are identified in the Code of Practice:

Equines that are sick, injured or in pain must receive appropriate treatment without delay or be euthanized without delay. 

For sick, injured or compromised horses that are not showing improvement, horse owners or caregivers must, without delay, obtain veterinary advice on appropriate care and treatment or make arrangements for euthanasia. 

Records or receipts for treatments provided must be available. Appropriate authorities must be advised of suspected or confirmed cases of federally reportable diseases, such as Equine Infectious Anemia. Refer to the Canadian Food Inspection Agency for more information.

These recommended practices are also provided in the Code of Practice:

  1. Learn how to take a horse’s vital signs. 
  2. Consult a veterinarian when vital signs are abnormal for an unknown reason or when a horse shows signs of illness. 
  3. Know in advance the route to the nearest veterinary hospital and have a plan in place for transport.
  4. Keep a first-aid kit on farm and in the transport vehicle.
  5. Consult an experienced horseperson or other expert for advice on safe restraint when treating a horse and provide an appropriate means of restraint when a veterinarian attends the horse.
  6. Have sheltered, segregated and well-bedded sick pens or stalls for horses that are sick, injured or recovering.
  7. Have isolation facilities available on the farm. 
  8. Monitor sick, injured and/or recovering horses at least twice daily.
  9. Ensure treatment records include a record of the animal(s) treated, date, reason for treatment, dosage, withdrawal time, if applicable, and any adverse reactions.
  10. Assign responsibility for health management decisions to a competent individual if you will be away from the farm for an extended period.


Colic, a painful gastro-intestinal disorder, has various causes, some of which are sudden changes of diet, internal parasites, stress, and lack of water. Colic is the most common digestive problem found in horses. Some horses are more prone to colic than others. The symptoms can develop slowly, so the earlier it is noticed, the better the chance of treatment. 

Horses can exhibit various symptoms. Stretching, rolling, repeatedly lying down or sitting on the hindquarters indicates that the horse is in considerable pain.

It is important that horse owners or caregivers know how to recognize the symptoms of colic in a horse.

Colic can be fatal. If colic is suspected, check the horse’s vital signs and listen for gut sounds.

Watch this video by Equine Guelph on how to listen for gut sounds in horses using a stethoscope:

If your horse is exhibiting signs of colic, call your veterinarian immediately. Follow their instructions until they can examine and treat your horse. 

Information adapted with permission from the “Horse Health” section of the 4-H Horse Reference Manual: Alberta Agriculture and Rural Development.

What does the Code of Practice for the Care and Handling of Equines say about colic?

“Colic is a sign of a painful condition in the horse’s abdomen. While episodes of colic vary in their severity, every case of colic should be taken seriously. The most common signs of colic are:

  • Repeated lying down, rolling and getting up, or attempting to do so
  • Turning the head toward the flank; kicking or biting at the belly; pawing at the ground
  • Stretching out as if to urinate, without urinating
  • Depression and/or loss of appetite 
  • Diarrhea or any change in manure output 
  • Sweating with minimal physical exertion.

To reduce the risk of colic: 

  • Provide safe, palatable, and clean water at all times
  • Maintain a consistent daily schedule for feeding, exercise and turnout 
  • Feed a high-quality diet comprised primarily of forage (limit the amount of grain-based feeds)
  • Divide the daily concentrate ration into two or more feedings
  • Avoid putting feed directly in contact with the ground especially on sandy soils
  • Ensure feed sources are free from mould and spoilage
  • Maintain a parasite control program in consultation with a veterinarian. Use fecal examination to confirm its effectiveness.”


The most common respiratory diseases are influenza, respiratory rhinopneumonitis and strangles. These diseases are spread easily through groups of horses. 

Symptoms of respiratory disease include:

  • Fever
  • Depression
  • Loss of appetite
  • Runny eyes and nose
  • Cough 
  • Swollen lymph nodes in the head, a symptom of strangles.

What does the Code of Practice for the Care and Handling of Equines say about infectious respiratory diseases?

“Young horses and horses that commingle with others, such as at a horse show or if living in high traffic barns, are at particular risk for respiratory infections, such as influenza, rhinopneumonitis and strangles. These infections can be spread in the air, by nose-to-nose contact or by contaminated hands, clothing, equipment and tools (e.g., feed buckets, water troughs and grooming tools). With some diseases, the infection can be spread by horses not showing clinical signs. 

Signs include fever, lethargy, nasal discharge, cough and swollen lymph nodes under the jaw (especially with strangles). Testing is often necessary to obtain a diagnosis. The time between exposure to infection and the occurrence of signs (known as the incubation period) varies from a few days to two weeks. Prolonged rest periods after infection are often needed to prevent chronic problems. While many horses recover uneventfully if managed properly, some horses can develop life-threatening complications. Horses showing signs of respiratory infection should be strictly quarantined and should not be worked until a diagnosis and a treatment/management plan have been established.

This recommended practice is provided in the Code of Practice:

  1. Isolate a horse with a suspected or confirmed communicable disease, get a diagnosis, provide treatment and alert any owners of horses that may have come in contact with that horse.
Excerpts from the Code of Practice for the Care and Handling of Equines (©2013) have been used with permission, Equine Canada and the National Farm Animal Care Council. 


Laminitis is an acutely painful inflammation of the laminae of the foot, commonly caused by overfeeding of grain, uterine infection, gastrointestinal problems, grazing of lush pastures, and total weight bearing by one leg because the other is lame.

This condition usually occurs in the front feet and is characterized by the horse trying to place most of its weight on the hind quarters with the fore feet extended forward. The horse may be unwilling to walk and exhibit a stilted gait. The horse may also be reluctant to pick up their feet. There may be increased heat in the feet or coronary band when palpated and a strong pulse might be felt at the pastern or fetlock.

Rapid treatment is necessary.

If you see these symptoms, call a veterinarian immediately. Apply ice packs to the feet or stand the horse in ice-cold water to reduce the temperature, and on a spongy surface to support the sole.

In severe cases of laminitis, the bone loses its attachment to the wall and the sole drops. Distinct lines or ridges appear on the wall. The coffin bone will rotate and come through the sole, which is very painful for the horse.

Information adapted with permission from the “Horse Health” section of the 4-H Horse Reference Manual: Alberta Agriculture and Rural Development.

What does the Code of Practice for the Care and Handling of Equines say about laminitis?

“Laminitis is a serious disease that causes inflammation in the foot that may result in severe pain, abnormal foot growth and lameness. If untreated or if treatment is unsuccessful, laminitis can lead to permanent structural changes in the foot, gait abnormalities, and continual or recurrent bouts of foot pain. The pain from laminitis can become severe enough to necessitate euthanasia on humane grounds.

Known or suspected causes of laminitis include grain overload, obesity, severe infections (such as severe diarrhea), Equine Metabolic Syndrome, “Equine Cushings” (PPID), and excessive concussion of the hooves. 

Diet plays a key role in triggering laminitis, particularly the consumption of pasture or feeds high in simple sugars, starches and fructans. Signs of acute laminitis include:

  • Lameness (including a cautious, stilted gait) 
  • Increased heat in the feet and/or a bounding pulse in the feet (felt at the pastern or fetlock)
  • Shifting weight to the hind end and front feet stretched out
  • Reluctance to pick up the feet.”

The following requirement is identified in the Code of Practice:

Horses with laminitis must receive appropriate lifelong management and treatment, which may include medications, dietary management and hoof care.

These recommended practices are also provided in the Code of Practice: 

  1. Reduce the risk of laminitis through the following strategies: 
  • Do not let horses get too fat – ensure they are at an ideal body condition score and are not overfed relative to their energy needs.
  • Ensure any changes to the diet are gradual.
  • Restrict at-risk horses from grazing on lush pasture (i.e., plentiful, bright green grass).
  • Store grains securely such that horses cannot gain access. In the case where a horse gains unrestricted access to grain, call a veterinarian immediately – do not wait for signs of laminitis to appear.
  1. Consult a veterinarian to determine special care that may be needed for a horse that has had laminitis. Horses that have had laminitis are at increased risk of developing the disease again and the condition can become chronic.
  2. Ensure communication between the veterinarian and farrier to determine whether corrective trimming or therapeutic shoeing may be needed.
LINK: You can learn more about laminitis by reading this factsheet by Equine Guelph.
Excerpts from the Code of Practice for the Care and Handling of Equines (©2013) have been used with permission, Equine Canada and the National Farm Animal Care Council. The process for the development of Codes can be accessed through the National Farm Animal Care Council.

Are you sure you want to log out?