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Laminitis will be a familiar term to most people who ride horses. For many it conjures up the impression of an overweight pony who develops painful feet a few hours after eating too much spring grass. Laminitis, however, is a very serious veterinary condition which can strike ponies and horses of any age and can have devastating consequences leading, in some cases, to the animals death. The simplest way of thinking about laminitis is a painful condition which is associated with damage and inflammation to the sensitive structures (laminae) of the horses foot. To understand the disease further we must think of it as condition with two components. The first phase of the disease, known as the acute phase, starts a few hours before lameness begins and continues as lameness develops over the first 48 hours. The second phase of laminitis, known as the chronic phase, occurs if the inflammation in the sensitive laminae persists for longer than 2-3 days. If the damage to the laminae is so serious that it causes death of the sensitive laminae tissues (necrosis) then the pedal bone may lose its firm attachment to the inner surface of the hoof wall and allowing the pedal bone to rotate.

Normal structure of the foot

We must know something about the normal equine foot and how its individual tissue function to be able to understand what happens when laminitis strikes. The hoof wall is a horny outer structure of the foot which grows down from cells in the coronary band and covers the outer layer of the foot. The hoof surrounds the pedal bone and is attached to it, on its inner surface, by a series of interlocking tissues called laminae. Since the foot is the structure supporting each limb, the entire body weight of the horse is supported by these laminal attachments within the foot. The laminae attached to the hoof wall have no blood supply and no pain receptors but the laminae that attach to the pedal bone are living tissues which require a blood supply and are richly provided with nerves. The blood to maintain these sensitive laminae comes from the two main arteries to the foot (palmar digital arteries) which branch into a very extensive capillary network throughout the foot before the blood flow rejoins the major veins that drain away from the foot. During evolution the horse has developed a series of vessels which bridge between the arteries and veins (arteriovenous shunt vessels) in the foot to enable blood to bypass the capillaries when necessary. These vessels are thought to be part of a mechanism to prevent heat loss in cold conditions. If anything abnormally disturbs the blood flow to the foot, either by preventing the blood from reaching the capillaries, or by opening up the bypass shunt vessels, it will deprive the laminae of vital oxygen and nutrition and resulting in inflammation within the laminae of the foot producing acute stage laminitis

What causes laminitis ?

It is thought that a sudden change in diet causes the normal bacteria in the colon (large bowel) to produce toxins that are released and absorbed into the blood stream. These toxins circulate around the body and have direct effects on blood vessels in many tissues causing the animals blood pressure to rise abnormally along with several other side effects. The most obvious direct effect of the circulating toxins, however, is the severe alteration in blood flow to the laminae of the feet with the pain and inflammation it causes. Any form of toxins released into the blood stream such as following a retained placenta, a severe uterine infection following a difficult foaling, toxic shock, peritonitis or liver disease can all have secondary effects on the laminae of the feet. The increase in circulating corticosteroids in horses with Cushings disease can also sensitise the blood vessels in the feet and can precipitate a laminitic attack.

Not all cases of laminitis are caused by disturbances of blood supply to the foot. Excessive concussion during road work can result in traumatic damage and inflammation of the laminae which will lead to laminitis. Horses with a long standing injury to one limb may have to carry an increased proportion of their body weight on their opposite good leg and can develop what is termed weight bearing laminitis - this is a complication seen occasionally in horses following surgery to repair fractures.

Treatment of acute phase laminitis

Whatever the underlying cause of the damage to the sensitive laminae, the treatment is directed to reducing the pain and suffering in the patient. Acute laminitis is, therefore, a veterinary medical emergency and the sooner the inflammation can be reduced the less damage will have been permanently done to the vital structures within the foot. If over feeding with concentrates or spring grass is considered to be the primary problem then the pony or horse must be moved to a stable or loose yard where its diet can be strictly monitored and controlled. In addition to reducing the diet, drenching the horse/pony with liquid paraffin may remove bacteria from the gut that are releasing the toxins. If a uterine infection is the cause then antibiotics and uterine wash-out would be appropriate. Administration of intravenous anti-inflammatory medication, by your veterinary surgeon, can help to reduce the pain and inflammation which will relieve the animals suffering and minimise the damage to the sensitive laminae of the foot.

Supporting the foot by transferring weight temporarily to the sole and frog and away from the damaged laminae can be very effective at relieving some of the discomfort. This can be most easily achieved by applying frog pads (Lilly pad) and moving the patient to a shavings\sand bed. The feet can be tubbed and cold hosed during the first few hours to reduce inflammation but contrary to older tradition it is now thought that animals suffering from acute laminitis should not be forcibly exercised since this just damages the sensitive laminae further.

Treatment of chronic phase laminitis

If the poor blood supply causes severe damage to the laminae the pedal bone rotates towards the ground. It is at this stage in the first attack of laminitis that the pony or horse is considered to have entered the chronic phase of laminitis. During chronic laminitis it is not the poor blood supply, but the mechanical forces, that are now causing the laminae to separate away from the horn wall. During this early phase of rotation it is crucial that the pony/horse is given a deep bed to encouraged lying down to rest the feet as much as possible until the rotation stops and the pedal bone position stabilises. Once rotation has occurred then the pedal bone cannot be returned to its previous position in the hoof capsule. The management of the chronic phase of laminitis is a very difficult problem which requires close collaboration between the veterinary surgeon and the farrier. Radiographs can be taken to demonstrate the degree of pedal bone rotation within the foot and this information can be used to allow the foot to be trimmed carefully so that the new horn, growing down from the coronary band, is encouraged to re-attach to the pedal bone in its new position. It often takes months of careful farriery to return the foot to a relatively normal appearance. Shoes should be fitted long and wide at the heels to give support to the foot in the area least affected by the damage to the laminae. The use of special shoes at this stage, such as the heart bar shoe or plastic glue on shoes can be valuable.

The old adage "No foot no horse" is particularly pertinent in the case of laminitis. Owners often consider laminitis as a minor problem because most animals that have mild attacks will usually improve rapidly but it is vital that the potential consequences are not forgotten.

Anvil Vets:

Anvil Equine Veterinary Clinic, Tuckmans Farm, Copsale, Horsham, West Sussex RH13 7DL

Tel: 01403 731 213 Fax: 01403 733992

Email anvilvets@freeuk.com

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