Laminitis
Laminitis is an extremely painful condition of the feet which causes severe lameness and is potentially a career or life-threatening situation. The pain results from inflammation of the sensitive laminae of the foot. This inflammation can lead to varying degrees of breakdown of these structures that attach the hoof wall to the bony structure of the foot. Just how this process occurs has been the topic of research for many years and recently some of the processes have become clearer.

There are several predisposing factors to developing laminitis. Among these are grain overload, grazing on pasture rich in carbohydrate, inflammatory diseases of the intestinal tract, retained fetal membranes and other endotoxic or septic conditions, toxins like black walnut shavings, and pain from injuries. Conditions that raise cortisol in the blood leading to insulin resistance such as Pars Intermedia Pituitary Dysfunction (Equine Cushing’s Syndrome), Equine Metabolic Syndrome for which may be some genetic predisposition, and lastly, administration of very large doses of corticosteroids also predispose some horses to laminitis. The commonality of this seemingly diverse list of causes is that they all result in a buildup of inflammatory chemicals and cells in the sensitive laminae of the hoof. There is a buildup of blood pressure, pounding pulses and warmth in the feet. Blood clotting particles may localize in the inflamed tissues. Glucose metabolism is disrupted and the cells begin to starve. The engorged and painful tissues begin to separate and break down.

In the worst cases the bone of the foot (the coffin bone, 3rd phalanx) actually rotates away from the hoof wall and can “sink” deeper in the hoof capsule as well. This is obviously a catastrophic occurrence.

Treatment of laminitis is difficult and often prolonged. It involves initial cold soaks, pain relief medication, antioxidants, proper hoof wall trimming, support shoes and specific dietary management.

Prevention of laminitis begins with dietary control. Minimize non-structural carbohydrates (NSC’s) in the diet. Grains such as corn, barley, oats, and wheat are all high in NSC’s. Lush grass is high in fructan, which is a carbohydrate that cannot be digested in the small intestine and is therefore passed to the hind gut where its fermentation can lead to alteration of the microflora and release of toxins. The carbohydrate content of grass is higher in the early growing season and specifically higher during the middle part of the day when photosynthesis is actively producing sugars. Fall grasses damaged by frost also can be high in stored fructans. Horses prone to laminitis or not used to free grazing should be limited in pasture access and grazing confined to early morning hours or at night.

Maintaining calories by adding digestible fiber such as beet pulp and the addition of fat to the diet are safe ways to maintain proper weight. Addition of fats such as corn oil, rice bran, and other oils actually aid in the proper metabolism of carbohydrate.

Prevention of laminitis also includes:
  • Reduction of stress and controlling pain from serious wounds or surgery to limit cortisol release. Prompt attention to colic, diarrhea, retained fetal membranes or other serious illness such as pleuritis also can fend off a laminitic episode.
  • Avoidance of obesity and regular foot care are also critical. Long flared hooves on a fat horse are a common finding in chronic laminitic horses.
The take-home messages are:
  1. Avoid obesity
  2. Avoid diets high in carbohydrate: 4-way, corn and barley, oat hay
  3. Treat stress-producing and infectious diseases promptly
  4. Suspected laminitis is an urgent situation to be addressed immediately
TREATMENT FOR ACUTE LAMINITIS
  1. COLD to reduce the inflammatory response—ice water boots for 48 hours have been shown to greatly reduce clinical laminitis if done at time of inciting cause.
  2. Anti-inflammatory drugs with pain relief
  3. Antibiotics (Polymixin B) to reduce bacterial toxins in cases of surgical colic.
  4. Possibly IV lidocaine to decrease white blood cell activation
  5. In the future, drugs to combat oxidative radical damage, including possible use of DMSO, especially since the equine hoof seems to have minimal laminar superoxide dismutase activity that would protect it against oxidative radical damage.
  6. Support of the foot. Acute cases need padding to allow movement—taping on blocks of blue board insulation or the use of commercially available heavily padded boots. Housing the horse in deep sand will provide sole support. Over time, shoes (glue-ons if needed early on) are used to bring the break over farther back to decrease dorsal hoof wall pressure, padding to support the back two-thirds of the sole and frog, and raising the heels with rails to decrease tension on the distal phalanx by the deep flexor tendon. The hoof is eventually trimmed to restore the alignment of the distal phalanx (P3) relative to the bearing surface.

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