What causes laminitis?

Understanding the risk factors for laminitis will help you to reduce your horse or pony's chance of developing this condition

Lush pasture is not the only cause of laminitis

Laminitis is an inflammatory condition of the hooves which causes pain and lameness in horses and ponies.

Laminitis can be classified into three main types depending on it's cause:

1) Hormonal Associated Laminitis (HAL)

This is the most common form of laminitis: 90% laminitis cases have an underlying hormonal condition such as Equine Cushing's disease (also known as Pituitary Pars Intermedia Dysfunction or PPID) or Equine Metabolic Syndrome (EMS)1. The exact mechanisms whereby these hormonal diseases cause laminitis is currently unknown, although both diseases are associated with high levels of insulin in the bloodstream (hyperinsulinaemia) which is known to cause laminitis.

2) Load-bearing laminitis

This occurs when severe lameness in one limb and the subsequent increase in weight-bearing of the opposite limb result in laminitis of that limb.

3) Toxaemic laminitis

This is where a septic condition, such as infection of the uterus, causes laminitis.

But what about grass?

Many horse owners believe that laminitis is caused by access to lush pasture. While grass is an important trigger factor, grazing alone does not tell the whole story. When a horse grazes their body produces insulin: normally this is an important mechanism which allows the horse to extract the energy and nutrients they need from the grass. The problem happens when a horse with hormonal disease already has high levels of insulin in their bloodstream or inappropriately produces too much insulin in response to feed intake; when this horse grazes the insulin levels in their bloodstream increase to very high levels. These extremely high levels of insulin cause laminitis. This is why some horses can develop laminitis whilst others grazing the same pasture do not.

Professor Andy Durham discussing the causes of laminitis

1. De Laat, M., Reiche, D., Sillence, M., McGree, J. (2019). ‘Incidence and risk factors for recurrence of endocrinopathic laminitis in horses’ Journal of Veterinary Internal Medicine 33(3), pp 1473-1482.

The simplest and most common test for Equine Cushing’s disease is the basal ACTH test.

To perform this test your vet will take a blood sample from your horse and send it to a laboratory that will measure the levels of a hormone called ACTH. The results of the test will then be compared to reference ranges (which change with the seasons) to confirm the presence or absence of Equine Cushing’s disease.

The measurement of serum insulin and glucose is often recommended alongside the basal ACTH test: These tests help to differentiate Equine Cushing’s disease from Equine Metabolic Syndrome (EMS) (another common hormonal cause of laminitis), and also act as an indicator of laminitis risk.

We are providing complimentary ACTH tests to horse owners who suspect their horse may have Equine Cushing’s disease. Simply generate a voucher code by clicking on the Free Test button on this page, and book a visit from your vet to find out whether your vet agrees that this test is appropriate for your horse.