Laminitis: No foot, no horse

The old saying, “no foot, no horse” still stands. The entire weight of a horse’s body is loaded onto its four feet when standing and onto only one foot when galloping. The foot is made up of multiple components, the deepest of which is the pedal bone (also called the coffin bone, distal phalanx or third phalanx). The pedal bone is attached to the inside of the hoof wall by 2 layers of sensitive laminae, one layer attached to the pedal bone (dermal laminae) and the other to the inside of the hoof wall (epidermal laminae). The laminae are made up of about 600 finger-like projections that interlock with one another maintaining the stability of the pedal bone within the hoof, similar to the action of velcro straps.

Laminitis or “founder” is the term used to describe the disruption of the connection between the pedal bone and hoof wall. If these sensitive laminae are damaged, the pedal bone can move within the hoof in either two ways. It can rotate due to the pull of the deep digital flexor tendon with the tip of the pedal bone rotating towards the sole or the entire pedal bone can sink downwards.

Clinical signs

Laminitis is extremely painful. Horses with an acute (rapid) onset of severe laminitis commonly show unwillingness or inability to walk and an increased respiratory rate. Affected horses often stand with the fore limbs “camped out” in front and the hind limbs under the body in an effort to take weight off the front feet. There is almost always increased digital arterial pulses detectable on both sides of the pastern region and the feet are hot to touch. In very severe cases, the horse will lie down a lot as it is too painful to stand. Commonly, both front feet are affected, but all four feet and even one singular foot can be affected depending on the cause.

In severe chronic cases of laminitis that have been going on for sometime, there may be an obvious depression around the coronary band which is evidence of sinking of the pedal bone. In mild chronic cases of laminitis, the clinical signs are similar but less pronounced. These horses are lame, but are still able to walk. There is usually increased digital pulses and mild heat in the affected feet. It is important to remember that damage to the sensitive laminae is irreparable, and horses that have suffered from laminitis previously, have a very high chance of foundering again. Horses that have suffered from laminitis are also more likely to suffer from foot abcesses and stone bruises than horses that haven’t.

If you suspect your horse has laminitis, try to move the horse, slowly, to a deeply bedded stall and ice/cold hose the feet. NEVER trot a horse when laminitis is suspected.

Diagnosis

Diagnosis of laminitis is best made by a veterinarian after a thorough clinical exam and a detailed history. Radiographs are helpful to determine the severity of pedal bone sinking/rotation, to aid the farrier devise a treatment plan and to assess the effectiveness of such a treatment protocol. Prevention, however, is always better than cure, but one must be fully aware of the causes of laminitis to prevent it.

Causes

There are a number of known causes of laminitis in horses which are included in the following list. The exact mechanisms by which they cause laminitis are unknown and research is still ongoing.

• Over feeding: excessive intake of carbohydrate from either grass or grain
• Trauma: working horses on hard ground without adequate shoeing can cause “road founder”
• Toxins in the bloodstream of ill horses (when a horse has diarrhoea, colic, colitis, retained foetal membranes, uterine infection)
• Excessive weight bearing: if a horse has been favouring one leg over another due to some degree of lameness, the favoured leg can develop laminitis due to excessive weight bearing. This is called supporting limb laminitis
• Corticosteroid associated laminitis. This includes:
  • Exogenous corticosteroids (those found in medications), and 
  • Endogenous corticosteroids (those which are naturally occurring in the body)
  • Increased levels of naturally occurring corticosteroids are found in horses suffering from equine metabolic syndrome (EMS), insulin resistance (IR) and equine Cushing’s disease (pituitary pars intermedia dysfunction)

Treatment

An acute episode of laminitis is considered a medical emergency and the main aim is to prevent or limit the extent of the damage to the sensitive laminae. This is achieved by cooling/icing the affected limbs in the early stages, padding the soles of the feet and/or putting the horse in a deep bedded box to prevent further trauma to the feet. Pain relief (usually phenylbutazone or flunixin meglumine) is very important. However, too much pain relief can have detrimental effects on the horses gastrointestinal system and on kidney function.

In the long term, corrective shoeing and trimming are the cornerstones of treating a laminitic horse. There is no cure for laminits, only strict management to help maintain a sound horse and to prevent further bouts of laminitis. It is critical that your vet and farrier work closely together to keep your horse sound.

Prognosis

Serial radiographs are the best indicator to monitor the progress of your laminitic horse. Unfortunately, it is not uncommon for some horses to be so severely affected that euthanasia is the only option.

Here are some practical tips to prevent laminitis from occurring in your horse.

1. Maintain your horses in an appropriate body condition, particularly in ponies, “cresty neck” horses, insulin resistant and untreated Cushing’s horses
2. Restrict intake of rich grass (e.g. in the spring and the autumn) by using a muzzle or keeping your pony on “scrub” pasture
3. Exclude high amounts of easily digestible grain from the diet
4. Store grain safely, where horses are unable to access it, even if they are loose!
5. Regular hoof trimming/shoeing by a recognised farrier
6. Avoid treating horses with any drug without prior consultation with your veterinarian
7. Cryotherapy. Cold hosing/icing has been shown to be effective against laminitis in the very early stages and at times when the horses are at a greater risk (e.g. after engorging on grain or retained placenta.)

Dr Ciaran Gobl

This content was originally published by Equine Veterinarians Australia (EVA), a special interest group of The Australian Veterinary Association.