Genetic health issues in horses
Over 350 horse breeds exist globally, with over a dozen native to the UK, after centuries of being bred for defining roles throughout history. While breeding for specific roles has produced distinct traits, it has also increased the prevalence of inherited genetic health conditions in some breeds.
On this page you’ll find definitions of different breed types, the associated health problems, and what to consider when choosing a horse or pony of your own.
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What are genetic health issues?
Genetic health issues are a result of a mutated gene or gene abnormality. Some genetic disorders have higher prevalence within certain horse breeds, which are then passed on, though some may occur due to spontaneous mutation. These disorders lead to health problems and suffering.
All horses can experience genetic health issues, although they occur more commonly in purebreds. Sadly, a lot of these horse genetic conditions – and the welfare issues associated – are an indirect result of breeding closely related individuals, resulting in limited genetic diversity. For example, weak immune systems (immunodeficiency), brain damage (cerebellar abiotrophy) and muscle paralysis (hyperkalemic periodic paralysis) are hereditary issues that affect certain horse breeds.
What is a purebred and pedigree horse?
Purebred horses have parents who are the same breed. Often, the two parent horses will have very similar ancestry, going back many generations.
As these horses are so closely bred (with a narrow gene pool), they’re at risk of developing numerous horse health issues.
The terms "purebred" and "Thoroughbred" are often confused, but they mean different things. While all Thoroughbreds are purebred, not all purebred horses are Thoroughbreds. A Thoroughbred is a specific breed of horse, best known for their use in horse racing.
In the horse world, it's more common to describe a horse as registered or purebred than as a pedigree horse. A purebred horse belongs to a single recognised breed, while a pedigree refers to its recorded ancestry or family tree. This will be documented in what’s known as a ‘stud book’ or a UK-recognised, breed-specific registry, in order to be verified.
Each breed is managed by its own breed society or registry, which sets the requirements for registration. In the UK, the General Stud Book records the ancestry of Thoroughbreds only, while other horse breeds maintain their own separate stud books or registries.
A closed stud book or registry is one that no longer accepts new horse breeds and only allows horses descended from already registered horses to be entered. An open stud book or registry accepts outsider bloodlines to strengthen the genetic diversity of the breeds. The risk of inherited disorders is closely tied to how a stud book is managed.
Important information
To stop diseases being passed from horse to foal, breeds known to have a higher risk of a genetic condition (known as a breed predisposition) shouldn’t be used in breeding programmes.
What is selective breeding?
Selective breeding is the practice of breeding horses with desirable characteristics so those traits are more likely to be passed on to their offspring. These traits can be physical, such as speed or strength, or behavioural, such as a calm and gentle temperament.
In the past, horses were bred for specific purposes; strength for farming activities, endurance for transportation, appearance as carriage horses, as participants in sports, or noble steeds in wars. Because of their many functions throughout history, selective breeding has led to a vast variety of breeds. Nowadays, many horses are also bred to become companions, for hobbyists and animal-lovers alike.
Today, horses continue to be selectively bred for traits such as athletic ability, conformation, temperament and breed standards. Selective breeding can also increase the risk of inherited genetic disorders if genetic diversity is reduced or harmful traits are repeatedly passed on through breeding, potentially impacting a horse’s quality of life.
What is a crossbreed horse?
A crossbred horse is one whose parents are from known different breeds. Parents may be purebred or crossbreeds themselves. Crossbreeding is a form of selective breeding practiced as a way to combine ideal traits, like colours, features or functions.
If the breed of the parents is unknown, this makes the horse a mixed breed, sometimes called a ‘part-bred’ horse.
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What health problems can these horses have?
Some inherited conditions are extremely painful, reduce the horse’s normal, everyday functioning and can even cause premature death. Others are very rare or cause minimal suffering. While purebred horses are more likely to develop some of these issues, all horse breeds can suffer.
Health problems of purebreds and pedigrees
Sadly, purebred horses are generally more likely than crossbred horses to develop certain genetic health issues because many breeds have closed stud books and reduced genetic diversity. Genetic health issues can sometimes become more common within a breed if they are linked to those traits or repeatedly passed on through breeding. For example, dwarfism is more common in some miniature horses because of selection for extremely small size.
Some breeds of horse with genetic conditions include Arabian horses, Miniature horses, Shetland ponies, Dales and Fell ponies, Friesians, Clydesdales, and Thoroughbreds.
From irritating issues to life-threatening conditions, associated horse health issues include:
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Tracheal collapse: This progressive condition affects the throat, causing it to weaken, and is reported more commonly in American miniature horses. Symptoms include wheezing coughs, dry ‘honking’ sounds and laboured breathing. Equine vets diagnose tracheal collapse through physical examinations, tracheoscopy, radiography or computed tomography (CT) scans. In severe cases, the condition can be fatal.
Cerebellar degeneration: This neurological condition causes parts of the brain to deteriorate. Commonly affecting Arabian horses, it’s present from birth, but may not be obvious until foals are around six months old. Signs include head tremors, lack of balance, wide-stance, and the inability to rise from a lay down position. As it has no cure or treatment, some horses with mild cases can be kept solely as non-ridden companions or are euthanised to prevent accidents as the condition is likely to get progressively worse over time. -
Hypotrichosis and mane and tail dystrophy: These inherited hair disorders affect normal hair growth, leading to symptoms such as thin, brittle or sparse coats, hair loss, and reduced or absent eyelashes and whiskers. While the conditions are not usually painful themselves, affected horses may be more vulnerable to issues such as sunburn and skin irritation due to reduced hair protection. Reported in some Arabians, Appaloosas and curly-coated horse bloodlines.
Hereditary equine regional dermal asthenia (HERDA): This condition causes fragile and slow-healing skin, in which outer layers can break easily and struggle to recover. Symptoms include loose and stretchy skin that can lead to lesions, scarring and blisters. There’s no specific treatment or cure for HERDA, and the more severe cases may commonly be euthanised, but horses can be maintained with proper management. HERDA commonly affects Quarter horses and related breeds from specific bloodlines.
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Severe combined immunodeficiency disorder (SCID): Often seen in Arabian horses, this is the lack of functional white blood cells, which are vital for a healthy immune system. Symptoms may include infections, nasal discharge, coughing, fever, pneumonia, colic, weight loss and diarrhoea. There is no cure for SCID, therefore, treatment is limited to supportive care. Foals with SCID often don’t make it past six months of age and may require euthanasia.
Hyperkalemic periodic paralysis: This muscle disorder causes muscle weakness, spasms and paralysis. Seen more frequently in younger horses (between two and three years of age), it’s strongly associated with Quarter horses, and its origins can be traced back to a Quarter horse born in 1969 named Impressive. It can be identified using DNA testing, and though there’s no cure, it’s manageable with diet, exercise and medication.
Chondrodysplasia (dwarfism): Occurring in some miniature horse and Shetland pony bloodlines, this group of inherited skeletal disorders affects normal cartilage and bone development, resulting in abnormal growth and proportions with signs including shortened limbs, enlarged heads and other skeletal abnormalities. Dwarf horses often suffer from breathing issues, joint problems and chronic pain, with many being euthanised to relieve suffering. Chondrodysplasia can be tested genetically to check if parent horses carry the gene before mating.
Glycogen branching enzyme deficiency (GBED): In this fatal condition, affected foals lack the enzyme used to store sugar molecules required by the heart, liver, brain and other muscles, leaving them unable to function. Symptoms include weakness, low body temperatures, limb deformities, seizures and respiratory failure. GBED is diagnosed via genetic testing, but blood work may also be required. Often seen in Quarter horses and other related breeds. -
Navicular syndrome:This painful condition affects the structures within the horse’s foot, particularly the navicular bone and surrounding tissues, and can lead to lameness and changes in movement. It’s not caused by a single inherited gene, but genetics may influence a horse’s risk through factors such as hoof shape and limb conformation. Breeding for certain conformational traits may increase susceptibility in some horses. Although there is no single cure, the condition can often be managed through veterinary care, pain relief, corrective hoof care and changes to exercise and management.
Many other pets face numerous other genetic health issues as a result of selective breeding – find out how this can cause suffering here.
Health problems of crossbreeds and mixed breed horses
Despite crossbreeds and mixed breed horses having a lower risk of developing some genetic diseases, they aren’t immune or automatically healthier. As the health and genetics of the parents can directly influence the health of their offspring, appropriate health screening tests should be carried out before breeding to reduce risk.
Preventing health problems in horses
Thankfully, some genetic diseases can now be tested for in advance. Genetic testing allows breeders and prospective horse owners to check for potential health risks in their horses, or the parents of a foal, and make informed breeding decisions. Tests also show if horses are carriers of genetic illnesses, but are not likely to suffer from this themselves.
Responsible breeding of any type of horse – crossbreed or purebred – can help prevent health problems in future horse generations, increasing genetic diversity and lowering the risk of inherited disease. This includes appropriate health testing, genetic screening where available, careful assessment of conformation, and selecting horses with sound temperaments and good overall health.
We believe that all those who breed horses, whether purebred, crossbred or mixed breed horses, should prioritise health, welfare and temperament over appearance. Responsible breeding protects the health and welfare of parents and their foals; which will always be more important than profit and the way they look. If we want our horses to be healthy, we must breed healthy horses.
What to think about when choosing a horse
Adoption is one of the most rewarding acts of kindness – for both person and animal.
We’ll always encourage rescuing horses over buying them. With hundreds of horses in our care – including ridden and non-ridden companions, ready to gallop into your lives – the chances are we’ve already found the perfect horse for you. Meet our rescue horses here.
However, if adoption isn’t possible and you decide to buy a horse, make sure to choose one well suited to your lifestyle and environment, from a responsible and reputable breeder.
Frequently asked questions
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Horses and ponies belong to the same species – Equus caballus. In general the main distinction between them is based on height and physical characteristics. Equines measuring 14.2 hands high (hh) or below are typically classified as ponies, while those above this height are usually considered horses.
