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Lifting the lid on Laminitis

Claire Gilbert MA, VetMB, MRCVS looks at the causes and implications of Laminitis

Laminitis affects nearly 10% of the equine population and can occur in horses, ponies and even donkeys, often with little or no warning. Rapid recognition of laminitis and prompt treatment are vital to reduce the severity of an attack. Recovery nonetheless often takes weeks or even months and recuperating laminitics require careful management as well as regular veterinary and farrier attention to give the best results.

Laminitic stance
Laminitic stance

Laminitis means inflammation (‘itis’) of the laminae which form the junction between the hoof wall on the outside and the foot including the pedal bone on the inside. The resulting laminar destabilisation may result in rotation or sinking of the pedal bone inside the hoof capsule.

The terminology of laminitis can be confusing, acute laminitis means a recent onset of the condition, it does not describe the severity which can range from mild to very serious. If the condition becomes longstanding or there are repeated bouts of acute laminitis it is described as chronic. “Founder” refers to mild or moderate pedal bone rotation or sinking, whereas “sinkers” are cases with major pedal bone displacement sometimes with the bone prolapsing through the sole.

The most common cause of laminitis, especially in ponies, is rich grass containing high levels of sugars, particularly fructans. Fructans are normally digested by large intestinal bacteria, but ingestion of large quantities leads to rapid fermentation and the production of toxic byproducts. These toxins are absorbed into the bloodstream and eventually cause damage and inflammation in the laminae. However there are many other causes of laminitis and it is sometimes difficult to establish why an individual has developed the disease.

Overweight animals can become insulin resistant due to their high body fat content and the resulting high insulin levels have recently been shown to cause laminitis. Equine metabolic syndrome (EMS) also leads to insulin resistance, this disease is usually seen in native ponies with subcutaneous fatty deposits and cresty necks. EMS can result in long term laminitis which is poorly responsive to treatment.

Severe acute laminitis with pedal bone rotation and sinking resulting in prolapse through the sole and an obvious gas shadow. Radiograph of a chronic laminitic foot showing pedal bone rotation and marked remodelling of the tip of the pedal bone.
Severe acute laminitis with pedal bone rotation and sinking resulting in prolapse through the sole and an obvious gas shadow.
Radiograph of a chronic laminitic foot showing pedal bone rotation and marked remodelling of the tip of the pedal bone.

Equine Cushing’s Disease is one of the most common diseases affecting older equines and causes symptoms such as a long curly coat, abnormal sweating, increased urination and laminitis. Cushing’s is caused by over-production of the hormone ACTH by the pituitary gland and leads to high cortisol levels which in turn cause laminitis. Other serious infections such as colitis and pleuropneumonia lead to laminitis if bacterial toxins enter the bloodstream.

Consumption of large quantities of grain, such as when horses gain access to a feedroom, generates huge quantities of lactic acid and toxins in the gut resulting in severe laminitis. In very lame horses, for example with a fractured limb, the opposite leg is forced to carry extra weight overloading the laminae and sometimes causing laminitis in this sound leg. Finally, corticosteroids drugs administered to treat various conditions such as osteoarthritis and allergies can in rare cases lead to laminitis.

Inflammation of the laminae which form the junction between the pedal bone and the hoof leads to weakening of these attachments. In mild cases of laminitis, treated correctly, the inflammation gradually subsides without the development of any structural changes. However in other cases the weight of the horse bearing down on the feet tears the laminar attachments resulting in sinking of the pedal bone within the hoof capsule, and the constant pull of the deep digital flexor tendon on the back of the bone leads to rotation. Laminar blood vessels are torn causing local haemorrhage under the hoof wall and creating a build up of painful pressure.

Checking the digital pulse strength
Checking the digital pulse strength

One of the most noticeable features of laminitis is lameness in several legs, the front feet are usually most severely affected and are generally similarly sore. The lameness is more apparent on hard ground with the horse being much more comfortable on a soft surface. At rest they will often stand with the forelegs out in front of the usual position and the hind legs tucked underneath the body and may shift weight from one foot to the other. The feet are warm to the touch and there are strong bounding pulses in the digital arteries which run down the sides of the fetlock. Hoof testers reveal sole pain in the toe region just in front of the frog and haemorrhage may be visible. In advanced cases there is a palpable depression over the front of the coronary band as a result of pedal bone sinking and occasionally the pedal bone can sink so far that the tip penetrates the sole just in front of the tip of the frog. The Obel grading scheme allows veterinary surgeons to classify the severity of a laminitic episode.

Lily pad for frog support
Lily pad for frog support

The priority in the initial treatment of laminitis is to support the pedal bone to prevent rotation or sinking. The shoes should be removed to allow better support to be applied to the sole and particularly the frog in the form of rubber or foam pads. The horse is stabled on a deep shavings bed in order that the bedding packs up under the foot to provide further support and cushioning. Ensure that the shavings extend right up to the doorway, a plank will prevent them falling out when the door is opened. It is important that the horse does not walk any more than necessary as movement will increase the strain on the laminae so box rest must be strictly adhered to. Horses which usually live out may become impacted when abruptly stabled, soaking the hay and feeding damp food or bran mashes for the first few days can reduce the risk. It takes several weeks for the laminar attachments to regain their strength and in most cases box rest will be necessary for at least a month, where there has been pedal bone movement this period may need to be significantly prolonged.

Painkillers such as 'bute' are prescribed to make the horse more comfortable and to reduce foot inflammation. Acepromazine is also commonly used to improve the blood supply to the laminae, its mild sedative action is useful to relax the horse and reduce movement. If there is an underlying cause, such as Cushing’s disease, it is important to implement treatment to eliminate the stimulus of the laminitic pathway.

Horses suffering from serious laminitic episodes may require a dorsal wall resection where a section of the front of the hoof wall is removed to release painful pressure, or grooving of the hoof wall which is a less invasive technique. Marked pedal bone instability and movement may force the veterinary surgeon to place plaster casts on the feet. If tension within the deep digital flexor tendon is compounding the situation then the tendon itself, or the check ligament which attaches to it, can be surgically cut to remove the rotation force.

Radiographs are necessary to fully assess the position of the pedal bone and the changes occurring within the hoof capsule. The images reveal the severity of laminitis which influences the treatment plan and gives a more accurate long term prognosis. The farrier can also use the radiographs to dress the foot more accurately and to position the shoes to provide optimal support.

In acute laminitis radiographs are used to identify rotation or sinking of the pedal bone which can be quantified for comparison with future images. There may also be gas and inflammatory fluid trapped under the hoof wall visible as a dark stripe. In chronic laminitics in addition to an abnormal position, the pedal bone may become distorted near the toe, known as remodelling, as a result of the rotation forces pulling on it. In serious cases there will also be loss of bone density and sometimes microfractures of the bone.

Metal heart bar shoe Plastic glue on heart bar shoe
Metal heart bar shoe
Plastic glue on heart bar shoe

Good farriery is essential in the treatment of laminitis, the foot must be carefully trimmed to gradually correct the orientation of the pedal bone relative to the ground. Once the acute inflammation has subsided heart bar shoes are often applied to support the pedal bone and stabilise the hoof capsule. Metal shoes are usually employed, but bad cases may benefit from glue on plastic shoes which are more gentle on the foot. Correction of laminitic changes is a slow process and the feet will need careful regular attention.

Deep shavings bed extending to front of stable
Deep shavings bed extending to front of stable

Once a horse has had laminitis they have an increased susceptibility to further episodes in the future so it is important that careful management is maintained in the long term.

Claire Gilbert MA, VetMB, MRCVS

(This article appeared in April 2010 edition of Central Horse News.)