Laminitis can affect any age or breed of horse, pony, donkey, or mule, and there are many potential causes. This article will focus on the most common cause of laminitis, i.e., disease that is caused by high levels of the hormone insulin, known as hyperinsulinaemia-associated laminitis (HAL) or endocrinopathic laminitis. We will not consider other triggers for this disease. These can include Potomac horse fever, excessive weight bearing following orthopaedic surgery, or retained placenta in mares.

HAL and Laminitis

Hyperinsulinaemia-associated laminitis can affect any horse. For many years, horse keepers have recognised that certain types of horses are at much higher risk. The condition usually occurs in mature adults of breeds such as British native pony breeds, Morgan horses, Andalusians, and to an extent Arabians and Warmbloods. These animals are often described as ‘good -doers’ or ‘easy-keepers.’

Affected horses and ponies are often kept at pasture or on a high-grain diet. Episodes of laminitis often coincide with changes in the quality of the pasture or other dietary and management changes.

It is not possible to prevent all cases of laminitis. However, horse keepers can reduce the risk to their horses by understanding more about those risks.

Physical Changes that Increase Risk

A higher risk of laminitis is associated with some specific physical features that are easily recognised.

Horses that are overweight are at greater risk. This is particularly true for those that carry the additional fat along the crest of the neck and/or as bulging fat pads just above the eyes.

This higher risk of hyperinsulinaemia-associated laminitis in overweight horses is often termed the equine metabolic syndrome (EMS) due to similarities with the ‘Metabolic Syndrome’ that occurs in people (sometimes known as ‘prediabetes’). However, there are also important differences between horses and people that affect the way the conditions are managed.

It is also very important for owners to be aware that not all cases of HAL will occur in overweight horses or the higher-risk breeds and these can also sometimes be described as suffering from EMS.

In fact, hyperinsulinaemia can occur in horses of all ages, breeds, and all levels of fat. Thin horses that are at increased risk of laminitis (sometimes termed ‘thin-EMS’) can be a particular challenge to manage and might benefit from additional veterinary and nutritional advice. 

Chronic Laminitis

In many cases, laminitis can be a longer-term condition than people realize. The signs of a severe laminitis episode are usually clear, but horses might have been affected by milder laminitis episodes for months or years before a severe episode occurs.

Learning to spot the more subtle signs of mild laminitis could help owners to prevent a severe episode.

Horses with mild laminitis might be slightly footsore on harder ground or after trimming. Their hooves might show signs of divergent growth in which the heels grow faster than the toes.

Farriers and trimmers might also see signs of mild stretching of the white line and bruising of the sole before severe signs become obvious.

Laminitis is also more common in horses with pituitary-pars intermedia disfunction (PPID) also known as equine Cushing’s disease. The condition can be diagnosed by blood tests (see below). It can be recognised by some common physical changes such as the characteristic delayed coat shedding and curly coat.

laminitis fat pony head and feet

Highest Laminitis Risk Times

Laminitis can strike at any time, but large-scale studies in the United States and Europe have shown the highest risk for horses at pasture is in the late spring/early summer. This is when the grass is at its richest.

To combat this, owners can monitor their horses more carefully. They also can manage their horses’ pasture turnout during periods of rapid grass growth.

For horses that are not kept at pasture, sudden changes in diet or a reduction in exercise can increase the risk of laminitis. If a horse requires a period of stable rest for an injury, then modifying its diet to account for the lower energy needs can be helpful.

Finally, the use of some steroid medications can trigger a laminitis episode in a horse that is at higher laminitis risk. When certain steroid medications are needed, veterinarians might wish to assess the laminitis risk depending on the type of steroid, the dose, and duration of treatment.

Blood Tests that Indicate Laminitis Risk

Testing the level of insulin in the horse’s blood is probably the most accurate way to assess the risk of hyperinsulinaemia-associated laminitis. The higher the insulin level, the greater the risk.

As horses get older, their insulin levels often increase. Therefore, monitoring insulin levels can be particularly important when caring for an older horse.

If high insulin levels are identified, then follow-up testing can be very useful to monitor any improvements as the condition is managed. For example, you can monitor the effect of dietary changes.

As discussed above, testing blood insulin levels can be particularly useful for identifying and managing horses that are at higher laminitis risk, such as ‘thin-EMS’ horses.

Insulin blood tests can be done in several different ways. Sometimes it is useful to investigate the horse’s insulin levels whilst it is eating a usual diet, pasture, or hay. In other cases, the response to a standard dose of sugar might be more useful (an oral sugar test).

Other blood tests can also help to confirm a diagnosis of PPID (equine Cushing’s disease), a condition that might contribute to higher insulin levels.

Final Words

Laminitis can affect any horse at any time. We hope to prevent cases by understanding the risks.

To reduce laminitis risk, owners can monitor their animals for signs of low-grade laminitis. They also can adjust feed and exercise to maintain a healthy body condition, and check the animals’ blood insulin levels.

Further Reading

  • Edward Knowles, MA, VetMB, MVetMed, PhD, is an equine internal medicine specialist with an interest in metabolic diseases of the horse. He currently is a postdoctoral researcher in Comparative Neuromuscular Disease at the Royal Veterinary College and as a specialist in Equine Internal Medicine at Bell Equine Veterinary Clinic (CVS Group plc).
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