Laminitis in horses

‘Laminitis’ is a word familiar to most horse owners, yet few are fully aware of the details of the condition, apart from the fact that it affects the feet and that once diagnosed can become a chronic problem.

What is Laminitis, and what does it mean?

The suffix ‘-itis’ on the end of a word implies inflammation, so dermatitis means inflammation of the skin, hepatitis is inflammation of the liver. Laminitis therefore means inflammation of the lamina – but what are the lamina? (plural = laminae).

The laminae are layers of strong connective tissue which join the inside of the horse’s hoof to the bone inside. The weight of the horse passes down through the long bones of the leg to the bone inside the hoof, (called the pedal bone). The pedal bone sits in the middle of the hoof, encased in the laminae which connects it to the inner lining of the hoof wall. Without this connective tissue support, the pedal bone would push downwards through the sole of the foot, which would obviously mean a catastrophic end to the horse’s ability to walk.

Inflammation of the laminae causes heat and swelling to build up inside the hoof. This is intensely painful, and the resulting lameness can be extreme. Severe episodes of laminitis in horses can cause the laminae to break down, losing the connection between bone and hoof and allowing the bone to rotate downwards, which is often life-threatening and always career-ending.

Causes of Laminitis in horses

Almost all cases of laminitis in horses arise from medical conditions which have nothing to do with the feet. 90% are due to a hormonal disorder called EMS, which stands for Equine Metabolic Syndrome. This condition is seen exclusively in obese horses and ponies. The accumulation of body fat in these animals causes insulin resistance – similar to the early stages of diabetes in people. This sets up a vicious circle of high blood sugar leading to more and more insulin production (which should reduce blood sugar but doesn’t). The high blood sugar ends up being stored as more fat which increases the obesity…… and we are back to square one! These horses and ponies often have an extreme appetite as the brain does not recognise that they have fully absorbed the sugars from the meal, so never switches off the drive to eat.

But how does this metabolic condition involving high blood insulin levels and obesity lead to problems in the laminae of the feet?  The answer to this question is not fully understood, but is likely to involve damage to the blood vessels of the laminae from chemicals produced by the disease process. It is a fact that almost all the cases of laminitis seen in fat ponies and horses are due to this extremely complex syndrome.

Another cause of laminitis in horses seen in Veterinary Practice is sepsis. This term refers to a severe bacterial infection in the bloodstream. The bacteria release toxins which directly attack the laminae, causing a particularly acute and severe form of laminitis. This is most often seen in mares which fail to pass the placenta after foaling, causing a womb infection which spreads to the bloodstream. Some gut infections can also cause sepsis and lead to acute laminitis. A horse which gorges on a grain feed can also develop a bacterial upset in the intestine which causes a similarly severe laminitis.

The third recognized cause of laminitis is aptly named. ‘Supporting Limb Laminitis’ occurs when an injury to one limb results in excessive weight-bearing on the opposite limb. The increased pressure on the ‘good’ foot can lead to inflammation and  breakdown of the laminae and subsequent pedal bone rotation. Horses recovering from limb surgery such as fracture repair are obviously at risk from this form of laminitis and preventative therapies are vital to ensure safe recovery. The 2006 Kentucky Derby winner ‘Barbaro’ succumbed to this condition after surgery on a hind leg.

Clinical Signs and symptoms of Laminitis in horses

Laminitis is usually seen in both front feet although hind feet may also be involved. The horse is reluctant to walk, particularly on hard or stony ground. It will have a shortened gait and it may be impossible to pick up a front foot for examination as the extra pressure on the other front foot causes intense discomfort. In more severe cases the horse adopts a ‘sawhorse’ stance, where the forefeet are stretched out in front to relieve the pressure, and the back feet brought forward to support the bodyweight. An examination of the feet will reveal heat in the affected hooves, a bouncing pulse in the blood supply to the inflamed foot, and pain if hoof testers apply pressure to the front part of the sole – commonly where the greatest pain is located.

In chronic cases where repeated bouts of laminitis in horses have occurred, the hoof may show rings of disturbed growth where the bouts of laminitis have prevented normal horn production from the coronary band. An X-ray of these chronic cases may show rotation of the pedal bone due to loss of connective tissue support. This carries a poor prognosis for complete ‘cure’ as the weight bearing mechanics of the foot have been permanently affected, and subsequent episodes of laminitis are more likely.

Management of Laminitis in horses

In cases where EMS is the underlying cause of the condition, weight loss is the primary aim. This can be difficult as these horses and ponies are likely to be genetically predisposed to weight gain – the so called ‘good-doer’ where even small amounts of food maintain an over-conditioned state. Overweight horses should not be starved as this can cause a sudden increase in fat mobilization which in itself can exacerbate insulin resistance. Weight loss is best achieved by a reduction in forage consumption to 1.5% of the horse’s bodyweight daily. If the hay is of high nutritional value it can be soaked to reduce the sugar levels before consumption. Access to grass must be strictly controlled or eliminated until a more appropriate body condition score is achieved. Walking exercise is beneficial but is not appropriate for those patients with acute laminitis.

Sometimes a human medicine called Metformin is prescribed by vets for EMS as it may help reduce insulin levels, though its effect may only be marginal. Some nutritional supplements are used to help increase insulin sensitivity and reduce appetite, and many owners have found these to be helpful. Ingredients naturally high in chromium are often included in these products, as research has suggested it improves insulin sensitivity in humans and helps to curb excess appetite.

Anti-inflammatory drugs are used to treat the foot pain and inflammation. Phenylbutazone (‘bute), may be prescribed in acute cases and to manage the discomfort of chronic laminitis, typically seen in older ponies with EMS. The age-old horseman’s remedy of standing the horse in a cold river has evolved into cryotherapy, where the application of crushed ice around the affected feet for 48 – 72 hours at the first signs of laminitis, has been shown to reduce damage to the laminae.

Providing additional support to the sole of the affected foot is vital in acute cases. This helps to ‘prop-up’ the pedal bone and prevent rotation. The simplest way to do this is to provide additional deep bedding such as sawdust, though in the longer-term special rubber pads combined with specialised shoeing techniques are the gold-standard.

Written by John Henderson MRCVS