Of the many skin conditions horses can develop, sarcoids are the most common. The term "sarcoid" was first used in 1936 in South Africa as a way to distinguish this skin lesion from other tumors. Sarcoids are benign (nonmetastatic) skin cancer believed to be caused by papillomavirus infection. They affect up to 11.5% of all horses. Sarcoids usually appear as rough, raised, hairless patches or nodules on the skin that are not painful or itchy. Some sarcoids are protruding, moveable masses with overlying skin still intact. The tumors are cosmetically unappealing and, depending on their location, can interfere with the function of the horse. But in most cases, the prognosis for affected horses is very good and some sarcoids resolve without any intervention. Effective treatments are available, including surgical removal, immunotherapy, cryotherapy, and laser surgery. However, sarcoids have a high rate of recurrence in horses.

Myofibrillar myopathy (MFM) is a newly identified muscle disorder that causes exercise intolerance in horses. MFM is a genetic condition that results from the abnormal build-up of desmin in muscle tissue. Desmin is a protein that is important for muscle contraction. In response to strenuous exercise, horses with MFM may experience pain, stiffness, lameness, poor stamina and intermittent gait abnormalities. This disorder has been identified mostly in Warmblood, Arabian horses and their crosses. Affected Warmbloods often refuse to collect under saddle while Arabians tend to have episodes of tying-up or extreme cramping.

Slobbers, otherwise known as slaframine poisoning or salivary syndrome, is a condition that causes excessive salivation or drooling in horses. It is relatively rare and usually occurs in outbreaks, with multiple horses affected at once. Slaframine intoxication is caused by horses consuming a fungus that grows on legume forages under wet and humid conditions. Horses who ingest infected pasture, hay or silage can develop clinical signs, including hypersalivation and difficulty swallowing. While many animals are affected by this fungus, horses are particularly sensitive. Outbreaks of slobbers have occurred in humid climates, including North America, Europe and South America. Slobbers is non-life threatening, but the drool hanging from an affected horse’s mouth is unsightly and can be a nuisance.

Glycogen branching enzyme deficiency (GBED) is a fatal disorder caused by a gene mutation found in the Quarter Horse and Paint Horse bloodlines. GBED causes abortion in late-term pregnancies, stillbirth or severe muscle weakness and eventually death in newborn foals. GBED prevents foals from properly storing sugars in the body. As a result, there is not enough energy to fuel the important organs and muscles of the body. This causes severe weakness and other clinical signs. Genetic testing for diseases is required for most QH and APH horses in breeding programs to ensure healthy offspring and prevent financial loss associated with losing a foal.

Horses are prone to a number of different skin conditions and diseases. Some are minor and resolve on their own, while others can be much more serious. Skin conditions may affect localized areas on the horse, such as the legs or abdomen, or they can be widespread, affecting multiple areas. Symptoms may include itchiness, swelling, hair loss, skin flaking, and more. Learning to recognize various equine skin diseases is important to take the appropriate actions needed to resolve the problem or to manage the horse to keep them more comfortable.

Equine grass sickness (EGS), or equine dysautonomia, is a rare and fatal disease in horses. It almost exclusively affects grazing horses kept on pasture. EGS is characterized by the development of severe lesions on the neurons of the peripheral and central nervous systems. Symptoms vary in severity depending on the neuronal degeneration in the horse. EGS results in loss of normal function of the gastrointestinal tract, affecting the horse’s ability to swallow and digest food.This disease results in a decrease in gut motility, increasing the risk of colic and causing severe weight loss. Although the exact cause of EGS is unknown, it is believed to result from a combination of environmental factors and bacterial infection.

Pain is something that all horses deal with at some point in their lives. Horses can experience pain for many different reasons, including injury, illness, or a result of surgery. For example, castration is the most common surgical procedure performed on horses and is associated with significant post-operative pain. Acute colic is another common painful experience for horses. Pain is also commonly associated with degenerative joint disease, laminitis, gastric ulcers, and hoof issues. Unlike humans, horses don't always show it when they are experiencing pain, or they may only display subtle signs of discomfort. This is because, as prey animals, they have evolved to hide signs of pain and weakness in the presence of predators.

Stringhalt, or equine reflex hypertonia, is a neuromuscular condition that causes abnormal hindlimb movement in the horse. Horses with stringhalt have excessive and prolonged flexion of the pelvic limbs while in forward movement, showing signs of the condition at most gaits. One (unilateral) or both (bilateral) legs may be affected. Some horses experience mild cases characterized by involuntary jerking of the hindlimb, while others experience lameness and difficulty standing up. Horses of all ages and breeds can be affected by stringhalt. In some cases, it is caused by ingesting toxic plants at pasture, but other cases develop quickly without apparent cause.

Bone spavin, also known as Degenerative Joint Disease (DJD) of the hock (tarsus), is an extremely common cause of equine lameness. It is caused by repeated concussion and rotational forces on the hock joint, as well as excessive forces on the adjoining ligaments. As a wear and tear condition, bone spavin is characterized by narrowed joint spaces and bone spurs. It is frequently bilateral and accompanied by lameness, with a decreased range of motion.

Equine herpesvirus (EHV), or rhinopneumonitis, is a contagious infection that is endemic to horses worldwide. EHV may cause mild to severe symptoms that usually involve the upper respiratory tract. In rare cases, it may cause neurological symptoms, abortion or death. Horses can experience latent infections of EHV where the virus lives dormant without causing symptoms. There are nine known types of herpes viruses in horses, of which EHV-1 and EHV-4 are the most common. EHV-1 usually results in more severe symptoms but EHV-4 is more common.

Botflies (Gasterophilus spp) are parasitic flies that affect the horse's digestive tract and can cause negative health consequences. Botflies lay eggs on the horse's coat in the summer. Some of these eggs, known as horse bots, are ingested as the horse licks and grooms itself. The bot eggs hatch and the larvae develop in the horse's mouth before migrating to the stomach where they attach to the gastric mucosa. Once mature, they detach and are passed through the manure. They pupate into flies, and the cycle repeats with new botflies seeking out horses to host their eggs.

Equine COPD - or chronic obstructive pulmonary disease - is a now-obsolete term for a common condition in horses that causes coughing and poor performance. This condition is now referred to as equine asthma and is one of the most common non-infectious lung diseases. Severe equine asthma affects 14–17% of horses in some populations, but up to 70% of pleasure horses have indicators of mild to moderate asthma. Horses affected by equine asthma typically have increased mucus production, difficulty breathing during exercise and sometimes at rest, cough, and nasal discharge. More severe cases may result in acute respiratory distress.

Equine asthma (EA) is a relatively new collective term for chronic respiratory signs in horses that range in severity from mild to severe. These conditions were previously known as inflammatory airway disease (IAD) or recurrent airway obstruction (RAO), respectively. Equine asthma is characterized by inflammation and mucous production in the lungs, which leads to lower airway obstruction. The horse may cough, and breathing may or may not be laboured. Asthma is most commonly observed in horses stabled over winter months that have become hypersensitive to dust, airborne allergens, mold spores, or mites in stable bedding or stored hay.