Understanding Diseases & Symptoms
Find knowledge not only by diagnosis, but by the questions horse owners actually ask.
Symptoms are clues. Knowledge brings orientation.
Usage note
This content is for information and education. It does not replace veterinary diagnosis or treatment. If your horse shows signs of illness, consult a veterinarian.
Start with owner questions
My horse has a problem — pick what you observe.
My horse has a skin problem
Skin & coat, allergies, gut, metabolism, grooming, sweet itch
My horse has digestive problems
Gut, microbiome, free faecal water, colic, gastric ulcers, parasites
My horse has metabolic problems
EMS, PPID, laminitis, liver, kidney, excess weight, coat change
My horse is lame or moves badly
Hooves, joints, tendons, muscles, back, osteoarthritis
My horse is coughing
Airways, management, dust, hay quality, allergies, immune system
My horse has allergies or immune issues
Immune system, skin, airways, allergens, inflammation
My horse shows neurological signs
Neurology, ataxia, headshaking, coordination, differential diagnoses
My horse has grown old
Senior Horse Health™, teeth, metabolism, mobility, cellular supply
My horse isn't performing
Sport, muscles, stomach, airways, electrolytes, recovery
My horse has a diagnosed condition
A–Z database, veterinary knowledge, studies, management, compounds
Systematic database
15 categories from Skin & Coat to Performance & Sport.
Skin & Coat
20Itching, rubbing, bald patches, flaky or inflamed skin — skin issues are rarely just skin.
Digestion & Gut
17Free faecal water, diarrhoea, recurring colic, a sensitive digestion — the gut is a central system.
Metabolism & Endocrine
15Excess weight, a tendency to laminitis, Cushing's, a burdened metabolism — endocrine topics affect the whole organism.
Hooves & Musculoskeletal
20Lameness, poor hooves, a stiff gait, back problems — movement is the interplay of many factors.
Respiratory
15Coughing, poor air, dust sensitivity — respiratory topics are closely tied to management and the immune system.
Liver, Kidney & Detox
13Raised liver values, metabolic strain, detoxification capacity — rarely to be viewed in isolation.
Immune System & Allergies
11Allergic reactions, recurring infections, constant sensitivity — the immune system is closely connected.
Neurology
13Ataxia, stumbling, coordination problems, headshaking — neurological signs need a clear work-up.
Heart & Circulation
10Rapid exhaustion, heart murmurs, circulatory weakness, declining performance.
Reproduction & Breeding
13Fertility, oestrus, pregnant mares, breeding management.
Infectious Diseases
22Contagious disease, isolation, vaccination, notifiable conditions — this is where clear structure counts.
Eyes
11Watering, half-closed or swollen eyes — many eye problems are emergencies.
Dental & Oral Health
13Eating poorly, dropping feed, weight loss, bad breath.
Senior Horse Health™
15Older horses involve several systems at once: teeth, gut, metabolism, movement, immune system, cellular supply.
Performance & Sport
16No performance, poor recovery, quick fatigue, no muscle development — performance is more than training.
All diseases (A–Z)
Search and filter by category, body system and urgency.
117 results
Acute Cough / Acute Bronchitis (viral or bacterial)
An acute cough is a symptom of suddenly arising airway irritation, often as part of a viral or bacterial infection of the upper and lower airways. It can be harmless and brief, but with fever, breathing difficulty or impaired general condition it may indicate a more serious infection and is often contagious in the stable.
Acute Eye Injury / Foreign Body (Trauma)
Blunt or sharp injuries and foreign bodies on the eye are painful and can acutely threaten vision. Even seemingly small injuries can reach deeper than visible and cause secondary damage (e.g. corneal ulcer, internal eye inflammation).
Anaphylactic Reaction (Allergic Shock)
Anaphylaxis is an acute, generalised allergic overreaction of the immune system (usually IgE-mediated) with massive histamine release. Within minutes it can threaten circulation and breathing and is a life-threatening emergency. Typical triggers are injections (medicines, vaccines, sera), insect stings or, more rarely, feed components.
Anhidrosis (Lack of Sweating / Impaired Thermoregulation)
Partial or complete loss of the ability to sweat, removing the horse's most important means of cooling. It occurs mainly in warm-humid climates and increases the risk of overheating under exertion.
Aortic Rupture
In aortic rupture, the wall of the great body artery (aorta) or a vascular structure near the heart tears, leading to massive internal bleeding. It occurs mainly in older breeding stallions and often in connection with exertion or covering, and frequently ends as sudden death — an acute emergency with no reliable means of rescue.
Atrial Fibrillation (AF)
Atrial fibrillation is an arrhythmia in which the heart's atria are excited in a disordered and very fast way, making the heartbeat irregular. It is considered the most common performance-limiting arrhythmia of the horse and often only becomes noticeable through declining performance, as the large equine heart can compensate for it at rest for a long time.
Bone Spavin (Osteoarthritis of the Tarsal Joints)
Bone spavin is a progressive, degenerative osteoarthritis of the small, tight hock joints (lower tarsal joints). Over time the affected joint surfaces can fuse, which often reduces the lameness again in the long run. It usually develops insidiously and frequently affects older horses or those heavily used over years.
Cataract
A clouding of the lens that restricts vision depending on its extent. Cataracts can be congenital, age-related or a consequence of other eye diseases (e.g. recurrent uveitis) and often run a chronic course.
Cerebellar Abiotrophy (CA, TOE1/MUTYH)
Hereditary disease of the cerebellum in the Arabian, in which specialised nerve cells degenerate prematurely. CA is inherited autosomal-recessive (marker in the TOE1 gene, regulatory effect on the neighbouring MUTYH); only homozygous animals are affected. Typical are coordination and balance disturbances that usually become apparent in foalhood and persist.
Cheek Tooth Fracture / Apical Tooth Infection
A cheek tooth can fracture or become infected at the root tip (apical infection). In the rear upper cheek teeth the roots reach into the maxillary sinus, so a root infection can trigger a secondary (dental) sinusitis. The findings are painful and need prompt veterinary clarification.
Chewing & Swallowing Difficulty in Old Age (dental insufficiency)
In the old horse, the lifelong erupting teeth eventually wear down, leaving gaps, loose teeth or missing cheek teeth (dental insufficiency). The horse can no longer chew its roughage sufficiently — it forms feed wads and drops them (quidding), the risk of choke rises and it slowly loses weight. With adapted feed management, many of these horses remain well supplied.
Choke (Esophageal Obstruction)
In choke, a feed bolus or foreign body blocks the esophagus so that feed and saliva cannot be swallowed. Unlike in humans, breathing is usually unaffected — nevertheless choke is an acute veterinary EMERGENCY.
Cholangiohepatitis / Bile Duct Inflammation (possibly with gallstones)
Inflammation of the bile ducts and adjacent liver tissue, often through an ascending bacterial infection from the intestine. Sometimes gallstones (cholelithiasis) are involved, hindering bile flow and triggering flare-ups.
Coat Change Disorders
The coat change is a metabolically intensive phase; a sluggish, delayed or incomplete change can indicate increased nutrient demand, metabolic strain or an underlying disease. In older horses, a delayed coat change is a classic warning sign of PPID (Cushing).
Colic Risk (Prevention)
Colic is an emergency with many causes — a substantial part of the risk factors lies in feeding and husbandry management and is controllable.
Conjunctivitis
Inflammation of the conjunctiva, the moist tissue around the eye and inner lid. It is common but should not be dismissed as harmless too quickly: veterinary clarification is important to reliably distinguish more serious causes (e.g. corneal ulcer, uveitis, foreign body, tear-duct problem).
Corneal Ulcer
A defect of the corneal surface that can range from superficial to deep into the corneal tissue. An ulcer is painful and sight-threatening: bacterial or enzymatic processes can worsen a 'melting' ulcer within hours to a few days, up to perforation of the eye.
CPL (Chronic Progressive Lymphoedema)
Chronically progressive disorder of the lymph drainage in the lower legs of heavily feathered breeds (among others Shire, Clydesdale, Belgian Draught, Tinker). There is increasing swelling, skin folds and nodule formation under the dense feathering; a hereditary predisposition for a disturbed elastin/connective tissue regulation is assumed. CPL is not curable but can be slowed by consistent management.
Cryptopyrroluria (KPU) — a debated topic
KPU is a term widely discussed in practice for a presumed metabolic/detoxification disorder, but it is NOT recognised in established veterinary medicine as a distinct, scientifically proven disease. Robust studies are lacking; the attributed symptoms are non-specific and can have many other causes.
Cryptorchidism (Undescended Testicle / Rig)
Congenital failure of one or both testicles to descend into the scrotum; the retained testicle lies in the inguinal canal or abdominal cavity. Affected stallions (rigs) often show stallion-like behaviour despite an apparently incomplete castration.
CSNB (Congenital Stationary Night Blindness, TRPM1)
Congenital impairment of vision in low light, linked to the leopard complex (LP) in the TRPM1 gene. Only homozygous animals (LP/LP) are affected — that is, those with the strongest leopard spotting. The impairment is congenital, stays the same lifelong and does not progress. In daylight affected horses see normally.
Cystitis (Bladder Inflammation, lower urinary tract)
Inflammation of the bladder lining, in the horse usually secondary — e.g. as a consequence of urinary stones, a urination disorder, bladder paralysis or after foaling/catheterisation. A primary, purely bacterial cystitis is comparatively rare in the horse.
Diarrhea
Diarrhea is a symptom, not a disease in itself, and ranges from harmless and transient to life-threatening. Acute, watery diarrhea with fever or apathy can indicate a serious infection and lead to dangerous fluid loss.
Diastema & Periodontitis (Food Pocketing, Gum Pockets)
A diastema is an abnormal gap between two neighbouring cheek teeth. Feed can become trapped in such gaps (food pocketing), inflaming the gums and periodontal apparatus (periodontitis). This is considered one of the most painful oral diseases of the horse.
Dorsal Displacement of the Soft Palate (DDSP)
In DDSP, the rear edge of the soft palate displaces over the epiglottis and temporarily obstructs the airways, especially at fast work. Typical is a gurgling breathing sound on exhalation with a sudden drop in performance; many horses start normally and only break down at high speed.
DSLD / ESPA (Degenerative Suspensory Ligament Desmitis)
Chronically progressive connective tissue disorder in which proteoglycans are pathologically deposited in tendons, ligaments and further tissues (hence also Equine Systemic Proteoglycan Accumulation, ESPA). Unlike a single tendon injury, DSLD is systemic and typically affects the suspensory ligament of several limbs. The disease occurs in familial clusters (among others Peruvian Paso), but the exact mode of inheritance is not conclusively clarified; DSLD is not curable.
Dwarfism (Friesian, B4GALT7)
Hereditary skeletal/connective tissue disorder of the Friesian through a mutation in the B4GALT7 gene (disturbed build-up of proteoglycans of the cartilage/connective tissue matrix), inherited autosomal-recessive. Affected foals show shortened limbs with relatively normal trunk/head size as well as overextensible joints. Only homozygous animals are affected; carriers are unremarkable.
Dysbiosis / Disturbed Microbiome
Dysbiosis describes a gut microbiome that has lost balance, e.g. after starch-rich feeding, antibiotics or abrupt ration changes. A stable microbiome is considered important for fibre digestion, nutrient supply and immune status; research on this is still young.
Dystocia (Difficult Birth / Foaling Complication)
A disturbed or difficult course of birth in which foal and/or mare are at risk without help — usually through malposition, malposture or malpresentation of the foal. In the mare the expulsion phase is exceptionally short and powerful, so any delay quickly threatens the life of mare and foal.
Electrolyte Loss & Thumps (Synchronous Diaphragmatic Flutter, SDF)
With long/intense exertion — especially in endurance sport — large amounts of electrolytes (including sodium, chloride, potassium, calcium) are lost through sweat. A visible sign of a severe shift is thumps: a diaphragm fluttering in synchrony with the heartbeat (synchronous diaphragmatic flutter, SDF).
Endocarditis (Heart Lining/Valve Inflammation)
In endocarditis, usually bacteria colonise the heart lining and especially the heart valves, forming inflammatory deposits there, so-called vegetations. These damage the valves, produce a heart murmur and can wash small infectious fragments into the circulation; the disease is serious and often runs with persistent or recurrent fever.
Endometritis (Uterine Inflammation in the Mare)
Inflammation of the uterine lining (endometrium), often through ascending germs after breeding, foaling or with disturbed self-cleaning of the uterus. One of the most common causes of subfertility (failure to conceive) in the mare.
EOTRH (Equine Odontoclastic Tooth Resorption and Hypercementosis)
EOTRH is a painful, progressive disease, mainly of the incisors and canines of older horses. Tooth substance is broken down by odontoclasts (resorption), while the body partly reacts with excessive cement formation (hypercementosis), bulging the tooth roots. The cause is not yet fully understood.
Equine (Grey Horse) Melanoma
The equine melanoma is a tumour of the pigment-forming cells that predominantly affects older greys (grey horses) — very common in old greys. Typical sites are the underside of the tail/dock, the anal region/perineum, the lips and the parotid (salivary gland) region. Many melanomas grow slowly over years and seem benign at first, but a considerable proportion can become malignant, grow invasively or spread — a reliable prediction is not possible from the outside.
Equine Asthma (RAO / IAD)
Chronic inflammatory airway disease caused by dust/mould allergens, with bronchospasm and increased mucus.
Equine Herpesvirus (EHV-1/EHV-4)
EHV-1 and EHV-4 are widespread, highly contagious herpesviruses of the horse. EHV-4 mainly causes airway infections, EHV-1 additionally abortion (viral abortion) and the feared neurological form (equine herpesvirus myeloencephalopathy, EHM). Once infected, horses carry the virus latently and can reactivate it under stress.
Equine Influenza (Horse Flu)
Highly contagious viral airway disease caused by the equine influenza virus (orthomyxovirus, type A). It spreads rapidly by droplets and typically causes sudden fever and a dry cough; with an uncomplicated course healthy horses usually recover, but premature exertion can prolong the illness.
Equine Protozoal Myeloencephalitis (EPM)
EPM is an inflammation of brain and spinal cord caused by protozoa (usually Sarcocystis neurona, less often Neospora hughesi) that can produce very varied neurological deficits. GEOGRAPHIC NOTE: EPM occurs mainly in North, Central and South America, because its definitive host — the opossum — is native there; in Europe and the German-speaking region it appears practically only in imported horses or returning travellers that were previously in the Americas. Horses become infected via feed or water contaminated with opossum faeces, not horse-to-horse.
Equine Recurrent Uveitis (ERU / Moon Blindness / Periodic Ophthalmia)
A recurrent, immune-mediated inflammation of the inner eye membrane (uvea) and the most common cause of blindness in horses. A role of Leptospira antigens and a genetic predisposition (e.g. Appaloosa, warmbloods) are discussed; every acute flare can further damage the eye.
Equine Sarcoids
Sarcoids are the most common skin tumours in horses — locally aggressive, fibroblastic skin growths associated with bovine papillomavirus (BPV-1/-2). They do not metastasise but tend to recur and can become more aggressive after irritation.
Exercise-Induced Pulmonary Hemorrhage (EIPH)
In EIPH, bleeding from small lung vessels into the airways occurs under high exertion, triggered by very high pressures in the pulmonary capillaries during intense work. It mainly affects racehorses and high-performance horses and often goes unnoticed, as only some horses show visible nosebleeds.
Exertional Rhabdomyolysis (Tying-up, RER)
Acute exercise-related breakdown of muscle fibres with painful stiffness, usually shortly after the start of work. Released myoglobin can darken the urine and burden the kidneys. The recurrent form (RER) is a disorder of muscle-contraction excitability and must be distinguished from the hereditary glycogen storage disorder PSSM.
Facial Nerve Paralysis
In facial nerve paralysis, the facial nerve (nervus facialis) is impaired on one or both sides, so that the mimic muscles of lip, nostril and ear no longer work properly. Common causes are pressure or trauma, e.g. from a too-tight halter, prolonged lying on hard ground or unfavourable positioning during anaesthesia. The typical picture is a drooping lip and a drawn-in nostril on the affected side.
Feed Allergy / Feed Intolerance
In a true feed allergy, the immune system reacts to a feed component, usually with skin or digestive symptoms. In horses, however, it is rare and often overdiagnosed — many supposed allergies are non-immunological intolerances or have other causes. Proof is demanding and best achieved through a controlled elimination diet.
Foal Sepsis & Failure of Passive Transfer (FPT)
Foals are born without their own antibodies and depend on taking up immune substances (IgG) from the first colostrum. If too little colostrum is taken up in the first hours of life (failure of passive transfer), immune protection is lacking — the main risk factor for a life-threatening blood poisoning (sepsis) of the newborn.
Free Fecal Water Syndrome (FFWS)
In free fecal water syndrome, free, often brown liquid is passed in addition to formed manure, soiling the tail and hindquarters. Causes are considered multifactorial and not yet scientifically settled; general condition is usually unaffected.
Gastric Ulcers (EGUS)
Damage to the stomach lining from acid load, feeding gaps, stress and starch-rich rations. Very common in sport horses.
Geriatric Weight Loss & Muscle Wasting (Sarcopenia)
Many older horses lose weight and especially muscle (sarcopenia) over time, particularly over the topline and hindquarters. This is almost always multifactorial — tooth wear, hormonal changes (PPID), declining feed utilisation, pain or competition in the herd act together. Weight loss in old age is not a normal part of ageing but a reason to look specifically for the causes.
Headshaking Syndrome (Trigeminal-Mediated Headshaking)
In headshaking, the horse involuntarily and often violently flicks or jerks its head, mainly vertically, in response to a painful hypersensitivity of the trigeminal nerve (facial nerve). A common form is light-triggered (photic headshaking) and is worse seasonally in summer and in sunlight. The syndrome is not a vice but a neuropathic process that can severely impair quality of life.
Heat Stroke & Exertional Hyperthermia
A life-threatening heat build-up when heat dissipation can no longer withstand the load and/or ambient heat — often combined with dehydration. Body temperature rises sharply and circulatory collapse is possible. This is an emergency.
Hepatic Encephalopathy / Hyperammonaemia
Neurological dysfunction as a result of liver failure: the damaged liver can no longer sufficiently detoxify ammonia and other metabolic products, which reach the brain. It is an acute crisis on the basis of severe liver disease.
HERDA (Hereditary Equine Regional Dermal Asthenia, PPIB)
Hereditary connective tissue disorder of the skin (collagen defect through a mutation in the PPIB gene), in which the skin layers are insufficiently anchored. HERDA is inherited autosomal-recessive and occurs above all in certain cutting/performance lines of the Quarter Horse; only homozygous animals are affected, carriers are clinically unremarkable.
Hives (Urticaria)
Acute, often allergic or pseudo-allergic skin reaction with suddenly appearing raised wheals. Can be harmless and transient but may recur — and is a warning sign with accompanying swelling or breathing difficulty.
Hoof Abscess
In a hoof abscess, pus accumulates within the non-expandable structures of the hoof capsule and creates painful pressure — typically a sudden, often severe lameness. Dramatic as it looks: after professional opening and drainage, the condition usually improves quickly.
HWSD (Hoof Wall Separation Disease, SERPINB11)
Hereditary disorder of hoof wall formation in which the wall separates from the pedal bone along the white line and breaks away. The cause is a recessive variant in the SERPINB11 gene; only homozygous animals are affected, carriers are healthy. Changes usually appear in the first year of life. Described above all in the Connemara pony.
Hydrocephalus (Friesian, B3GALNT2)
Hereditary developmental disorder of the Friesian with pathological accumulation of cerebrospinal fluid and a strongly enlarged skull of the foal, caused by a mutation in the B3GALNT2 gene and inherited autosomal-recessive. Affected foals are mostly not viable (often stillbirth); the enlarged head additionally means a considerable risk for a difficult birth (dystocia) and thus a danger for the mare.
Hyperlipemia / Fatty Liver
In hyperlipemia, mobilised fatty acids flood the blood and are deposited as fat in the liver — triggered by a negative energy balance (feed refusal, stress, pregnancy/lactation). Ponies, donkeys and miniature horses are especially affected; the course can be life-threatening.
HYPP (Hyperkalaemic Periodic Paralysis, SCN4A)
Hereditary dysfunction of a sodium channel of the skeletal musculature (SCN4A) that leads to episodic muscle weakness up to paralysis. The trait originates from the Quarter Horse stallion line Impressive and is inherited autosomal-dominant, so even heterozygous (N/H) horses can show symptoms. A high potassium content in the feed is a central trigger of episodes.
Immunosenescence (age-related decline of immune defence)
With age, the horse's immune system changes: defence reacts more slowly and less specifically, while a low-grade chronic inflammatory tendency rises (inflammaging). As a result, older horses can be more susceptible to infections, heal more slowly and respond more weakly to vaccinations. A concurrent PPID disease can further intensify these effects.
Insulin Dysregulation / Insulin Resistance (ID/IR)
Insulin dysregulation is a disturbed sugar/insulin metabolism with an excessive or sustained insulin response, often the core of EMS. It is considered a central risk factor for endocrinopathic laminitis and is objectified via blood diagnostics.
JEB (Junctional Epidermolysis Bullosa, LAMC2)
Hereditary disorder of the anchoring between epidermis and dermis. In homozygous foals the skin detaches over large areas at the slightest friction, as does the hoof horn. In the Belgian draught breeds the cause is a variant in the LAMC2 gene. Carriers are completely healthy; the trait is unambiguously identifiable by gene test and therefore avoidable.
Kissing Spines (Overriding Dorsal Spinous Processes / ORDSP)
In kissing spines, the dorsal spinous processes of neighbouring thoracic/lumbar vertebrae lie too close together or touch, which can cause irritation and back pain. Important: a radiographic finding alone does not necessarily mean discomfort — the overall picture of imaging and clinical signs is decisive.
Laminitis & Equine Metabolic Syndrome (EMS)
Insulin dysregulation with a tendency to obesity and a high risk of endocrinopathic laminitis. Common in easy-keeper breeds/ponies.
Lavender Foal Syndrome (LFS / CCDL, MYO5A)
Severe hereditary neurological disease of the newborn Arabian foal (also Coat Color Dilution Lethal), caused by a mutation in the MYO5A gene and inherited autosomal-recessive. Affected foals show the most severe neurological disturbances directly after birth and are not viable; often a diluted (lavender/silvery-pink) coat colour is noticeable at the same time.
Liver Disease (Hepatopathy)
Umbrella term for liver dysfunction of various causes (toxins, infection, metabolism). The liver has a high regenerative capacity.
Lyme Borreliosis (tick-borne)
Equine Lyme borreliosis is transmitted by ticks via bacteria of the Borrelia burgdorferi complex. Many horses carry antibodies without ever falling ill — attributing symptoms to an active borreliosis is diagnostically demanding and professionally disputed. The clinical picture is considered non-specific and is classified neutrally and cautiously.
Lymphangitis (Cellulitis, Phlegmon)
Lymphangitis is a painful inflammation of the lymph vessels and surrounding tissue, usually in one hind leg, with marked swelling. Triggers are often bacterial infections via small skin lesions (e.g. with mud fever), more rarely non-infectious/immune-mediated processes. It runs acutely, is very painful and tends to recur.
Mange / Mites (Chorioptes/Sarcoptes)
Skin disease caused by parasitic mites (often Chorioptes on the pastern/lower leg, less often Sarcoptes/Psoroptes) with intense itching, scaling and crusts. Mange is contagious and often transmitted via contact or shared equipment.
MCOA (Multiple Congenital Ocular Anomalies, PMEL17 / Silver)
Congenital malformations of the anterior eye segment, closely linked to the silver variant of the PMEL17 gene — that is, to the colour for which breeds such as the Rocky Mountain Horse are known. Heterozygous silver carriers usually show only iris cysts of no clinical significance, homozygous animals clear malformations up to visual impairment. The condition is congenital and non-progressive.
Mineral Imbalances
Not only deficiency but also an imbalance of major and trace elements (e.g. the ratio of copper to zinc or calcium to phosphorus) can affect skin, horn, muscle and metabolism. Since hay varies strongly by region, imbalances are best assessed via ration and blood analysis.
Mud Fever / Pastern Dermatitis
Umbrella term for an inflammatory skin reaction in the pastern fold with weeping, crusty or fissured areas. Usually multifactorial (wet, dirt, friction) and can be complicated by bacteria or mites.
Muscle Fibre Tear / Strain (acute sports injury)
Acute overstretching or a tear of muscle fibres, usually from sudden peak load, a misstep or insufficient warm-up. Unlike tying-up, the damage is locally confined; a correct diagnosis and controlled healing are decisive.
Myocarditis (Heart Muscle Inflammation)
In myocarditis, the heart muscle itself becomes inflamed, often following viral or bacterial infections or through toxic influences. The inflammation can weaken the pumping power and trigger arrhythmias; it is a serious disease that can lead to heart failure and belongs under veterinary monitoring.
Naked Foal Syndrome (NFS, ST14)
Hereditary disorder of the skin barrier in the Akhal-Teke. Homozygous foals are born without a coat; the skin barrier is incomplete, fluid loss and infections follow. The cause is a recessive variant in the ST14 gene. Carriers are healthy and normally coated.
Navicular Syndrome (Podotrochlosis)
Podotrochlosis is a chronic complex of changes to the navicular bone, bursa and deep flexor tendon in the navicular region, often leading to a shifting forelimb lameness. The causes are considered multifactorial (e.g. load, hoof shape, biomechanics); the syndrome is usually not curable but can often be managed for a long time.
Nervousness & Stress
Heightened spookiness/inner restlessness — often multifactorial (housing, management, deficiency, pain). Rule out behavioural causes first.
Ocular Squamous Cell Carcinoma (SCC)
Squamous cell carcinoma is the most common tumour of the horse's eye and mainly affects the lids, conjunctiva and the cornea-conjunctiva border. It is promoted by UV radiation and unpigmented (pink) lid margins — early clarification of suspicious changes is important.
OLWS (Overo Lethal White Syndrome, EDNRB)
Hereditary malformation of the intestinal nervous system in foals born pure white to spotted parents. The cause is a variant in the EDNRB gene: heterozygous carriers are completely healthy and show the frame overo pattern, while homozygous foals have no functioning intestinal nerve cells and cannot move the gut contents along. The trait is unambiguously identifiable by gene test — which makes the case entirely avoidable.
Oral / Mucosal Injury (bit- or foreign-body-related)
Injuries to the oral mucosa, tongue, bars (toothless jaw area) or lips often arise from ill-fitting or harshly used bits, sharp tooth edges or foreign bodies (e.g. wood splinters, awns). They are painful and can markedly impair eating and contact with the bit.
Osteoarthritis (OA)
Degenerative, progressive wear of the joint cartilage with an inflammatory and painful component. Common in older or heavily worked horses.
Overtraining Syndrome (chronic performance decline)
A persistent mismatch of load and recovery that leads to declining performance, poor regeneration and altered behaviour. It is a diagnosis of exclusion — other diseases (pain, stomach, airways, metabolism) must be ruled out first.
Overweight / Obesity
Overweight is widespread in leisure horses and not a cosmetic issue: excess body fat is metabolically active and raises the risk of insulin dysregulation and laminitis. The Body Condition Score (BCS) helps to assess condition objectively.
Pemphigus Foliaceus (autoimmune skin disease)
Pemphigus foliaceus is the most common autoimmune skin disease of the horse. The immune system forms antibodies against connecting proteins of its own epidermal cells, so that skin layers detach and pustules, crusts and scales form. The changes often start on the head, legs or lower abdomen and can spread.
Photosensitisation (Light Dermatitis)
In photosensitisation, the skin overreacts to sunlight because light-active substances (photosensitisers) in the skin release UV energy and damage tissue. Mainly unpigmented, white skin areas are affected. A primary form (photosensitisers directly from plants) is distinguished from a secondary, liver-associated form, in which a damaged liver no longer sufficiently excretes a chlorophyll breakdown product (phylloerythrin).
Pleuropneumonia / Shipping Fever
Pleuropneumonia is a severe bacterial infection of the lung and pleura, in which inflammation and fluid/pus accumulate in the chest cavity. It often occurs after long transports with a fixed, raised head (shipping fever) and is a potentially life-threatening disease that must be treated quickly by a vet.
PPID (Equine Cushing's Syndrome)
Dysfunction of the pituitary gland (pars intermedia) with hormone dysregulation, mainly in older horses. Raises the laminitis risk, among others.
PSSM (Polysaccharide Storage Myopathy)
Hereditary muscle metabolism disorder with abnormal glycogen storage; manifests as exercise-related muscle problems (tying-up).
Purpura Haemorrhagica (immune-mediated vasculitis)
Purpura haemorrhagica is an immune-mediated, necrotising inflammation of small blood vessels (type III hypersensitivity). It classically appears about two to four weeks after a strangles infection (Streptococcus equi) or, more rarely, after vaccination/other infections, when the immune system damages the vessel walls with cross-reacting complexes. Typical are extensive oedema and pinpoint mucosal bleeding.
Pyrrolizidine Alkaloid Liver Damage (Ragwort, Senecio etc.)
Chronic liver damage from pyrrolizidine alkaloids (PA) in poisonous plants such as ragwort/groundsel (Senecio), hemp agrimony or comfrey. Intake often goes unnoticed via hay/silage, in which dried plants lose their bitter taste; the damage is insidious and cumulative.
Quality of Life, Multimorbidity & Humane End-of-Life Care in Old Age
Very old horses often carry several chronic burdens at once (multimorbidity) — such as osteoarthritis, PPID, tooth loss and declining condition. This entry is not a single disease but a framework for honestly assessing quality of life: how are pain, mobility, eating and social contact? It also includes thinking in time and with empathy about the vet-guided decision to say goodbye.
Rain Rot (Dermatophilosis)
Bacterial skin infection caused by Dermatophilus congolensis that flares up with persistent wetness. Typical are crusty, paintbrush-like matted hair tufts along the topline; bald patches appear after the crusts come off.
Renal Insufficiency (acute & chronic kidney failure)
Impaired kidney function in which urinary metabolic products rise in the blood (azotaemia). It occurs acutely — e.g. after severe dehydration, shock, toxins or an overdose of painkillers — or develops chronically and insidiously; overall it is rarer in the horse than in small animals.
Retained Placenta (Retentio secundinarum)
Absent or incomplete passing of the placenta (fetal membranes) after foaling. Unlike in the cow, this is an emergency in the horse: if the placenta does not pass completely within a few hours (rule of thumb about 3 hours), life-threatening uterine inflammation (metritis), endotoxaemia and, as a consequence, laminitis threaten.
Ringworm (Dermatophytosis)
Contagious fungal infection of the upper skin layers (usually Trichophyton/Microsporum) with circular, scaly, hairless patches. Highly contagious between horses and transmissible to humans (zoonosis).
Roaring / Recurrent Laryngeal Neuropathy (RLN)
In roaring, the nerve supply to the laryngeal muscles — usually on the left side — is impaired, so that a vocal-fold cartilage does not open sufficiently on inhalation. This narrows the airways under exertion and produces the typical whistling breathing sound; large horses are especially affected.
Sand Colic (Sand Enteropathy)
In sand colic, ingested sand accumulates in the large intestine and can cause irritation, diarrhea, impaction or painful colic. Acute colic is always a veterinary EMERGENCY — sand accumulation can become life-threatening.
SCID (Severe Combined Immunodeficiency, DNA-PKcs/PRKDC)
Hereditary, severe defect of the immune defence in the Arabian foal: through a mutation in the DNA-PKcs gene (PRKDC) functional B and T lymphocytes are not formed. SCID is inherited autosomal-recessive; affected foals are practically defenceless against infections after the maternal antibodies from the colostrum are used up. The disease is not curable, affected foals usually die in the first months of life.
Sharp Enamel Points / Dental Hooks
Horse teeth grow throughout life and wear down through chewing. Because the upper jaw is wider than the lower, sharp enamel points form on the outer edges of the upper and the inner edges of the lower cheek teeth, which can press into the cheek or tongue. They are among the most common findings at a routine dental check.
Shivers (Shivering, neuromuscular movement disorder)
Shivering (shivers) is a usually slowly progressive neuromuscular movement disorder that mainly affects large horse breeds. Typical are involuntary twitching and an overextended, trembling posture of the hindquarters, especially when backing up and lifting the hind legs (e.g. for hoof picking or shoeing). The exact cause is not conclusively clarified; changes in the cerebellum (Purkinje cells) are discussed.
Sinusitis (Inflammation of the Paranasal Sinuses)
In sinusitis, one or more of the air-filled paranasal sinuses become inflamed, often with an accumulation of secretion or pus. It arises primarily after airway infections or secondarily through diseased cheek-tooth roots whose tips reach into the maxillary sinus.
Strangles (Streptococcus equi subsp. equi)
Strangles is a highly contagious bacterial infection of the upper airways and lymph nodes caused by Streptococcus equi subsp. equi. Typical are fever, purulent nasal discharge and painfully swollen, often abscessing throat lymph nodes. Most horses recover, but some become inconspicuous long-term shedders that carry the pathogen onward.
Strangulating Lipoma (pedunculated lipoma as a senior colic cause)
A lipoma is a benign fatty nodule that can form in the abdomen on the suspensory band of the intestine (mesentery). In older horses and ponies such a lipoma often hangs on a cord-like stalk — if this stalk wraps around a loop of intestine, the gut is strangled and cut off from its blood supply. This is an acute, highly painful and often surgical colic emergency.
Stringhalt
Stringhalt is a movement disorder in which one or both hind legs are jerked up exaggeratedly high during protraction, sometimes towards the belly. It is a neuromuscular disorder; besides a classic, often one-sided form, there is a pasture-associated (Australian) variant linked to the intake of certain plants — mainly flatweed (Hypochaeris radicata), less often vetches or Lathyrus species — that can affect several horses of a herd.
Sweet Itch (Summer Eczema)
Allergic skin reaction (hypersensitivity to the saliva of biting midges) with intense itching, mainly at the mane crest and tail base.
Tendon & Ligament Injury (Tendinitis / Desmitis)
Damage to tendons (e.g. superficial/deep flexor tendon) or ligaments (e.g. suspensory) through overload or acute trauma. Tendon tissue heals slowly and scars with inferior, less elastic replacement tissue — relapses are common, so consistent, controlled rehabilitation is decisive.
Tetanus (Lockjaw, Clostridium tetani)
Tetanus is a life-threatening disease caused by the soil bacterium Clostridium tetani. Spores enter the body through the smallest wounds, and their toxin makes the muscles cramp. Horses are especially sensitive and the course is often fatal — vaccination (primary immunisation and booster) is the decisive protection.
Thrombophlebitis (vein inflammation with thrombus)
In thrombophlebitis, a vein wall becomes inflamed and a blood clot (thrombus) forms in the vessel, in horses most often in the jugular vein. It often arises after venous catheters, injections or irritant medications and is usually clearly visible; with occlusion or infection of the vessel, complications threaten.
Thrush
Thrush is a bacterial (often anaerobic) decomposition of the frog horn, arising mainly in wet, dirty conditions and with poor hoof hygiene. It is recognised by black, greasy deposits and a putrid smell in the frog clefts; with superficial involvement it is usually well controlled through management.
Urinary Stones / Urolithiasis (bladder and kidney stones)
Formation of concretions in the urinary tract, in the horse most often bladder stones of calcium carbonate. This is favoured by the naturally alkaline, mineral-rich equine urine; geldings and older horses are over-represented. An obstruction of urine flow can become close to an emergency.
Valvular Heart Disease / Valve Insufficiency
In valvular heart disease, one or more heart valves no longer close fully, so blood flows back (insufficiency) and a heart murmur becomes audible. The most common form is degenerative thickening of the mitral or aortic valve, often an incidental finding on auscultation; many horses remain able to work for years, while advanced cases can limit performance.
Viral Abortion / Abortion (mainly EHV-1)
Premature death and expulsion of the foetus. One of the most important infectious causes is the equine herpesvirus (EHV-1), which can trigger single abortions up to abortion storms in the herd. Abortion material and amniotic fluid are highly contagious.
Warmblood Fragile Foal Syndrome (WFFS, PLOD1)
Hereditary connective tissue disorder of the Warmblood through a mutation in the PLOD1 gene (disturbed collagen cross-linking), inherited autosomal-recessive. Affected homozygous foetuses are mostly aborted or come into the world with extremely vulnerable, tearing skin and overextensible joints; the form is regarded as predominantly lethal. Carriers are clinically unremarkable and relatively frequent in Warmbloods.
Weak Hoof Horn (brittle horn)
Poor horn quality with brittle, splitting horn and shoeing problems. Grows only slowly (~6–9 mm/month) — patience needed.
West Nile Virus (West Nile Fever, neurological)
West Nile virus (WNV) is a mosquito-borne virus that can cause inflammation of the brain and spinal cord in horses. Most infected horses show no symptoms; if a horse becomes neurologically ill, however, the course is serious and a substantial proportion die or must be euthanised. A vaccine is available.
Wobbler Syndrome (Cervical Vertebral Malformation, CVM)
In wobbler syndrome, a malformation or instability of the cervical vertebrae narrows the spinal canal (stenosis) and thus compresses the spinal cord. The result is a usually progressive ataxia (incoordination), often in young, fast-growing large-breed horses. SAFETY NOTE: ataxic horses are unpredictable in movement and handling and can fall — riding and close handling carry a considerable injury risk for human and animal.
Wolf Teeth
Wolf teeth are small, vestigial teeth sitting directly in front of the first cheek tooth — usually in the upper jaw and not present in every horse. They are harmless in themselves but can cause pressure and irritation where the bit lies, which is why they are often removed before backing.
Worm Burden / Intestinal Parasites
Horses practically always carry some worm burden; only a high or damaging infestation (e.g. small strongyles, ascarids, tapeworms) becomes problematic. High burden can cause digestive disorders, weight loss and an increased colic risk — growing dewormer resistance makes a controlled approach important.
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