Laminitis (cont'd)
Acute Laminitis:
Acute laminitis occurs anywhere from 24 to 72 hours after the initial damage to the basement membrane and is heralded by the clinical signs of pain. Signs of acute laminitis include:
- severe lameness, reluctance to move, or even recumbency
- typical stance to try to get weight off the toes: front feet out in front if only the forelimbs are involved; all four legs in under the body if all limbs are involved; pointing with a leg if only one limb is involved
- increased digital pulses are almost always present (Fig. 4)
- heat in the foot; an unreliable measure because the temperature of the foot changes throughout the day; however, continued heat is often present with laminitis
- pain to pressure or percussion over the toe area
- systemic changes; anorexia, anxiety, increased respiration and pulse rates are often seen
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(Fig. 4) The presence of arterio-venous anastomoses (AVAs) gives an alternate route for blood passing from the arteriole to the venule. When the AVA is open, blood can bypass the capillary bed and is unavailable to the tissues. Prolonged opening of AVAs in the digital circulation may be important in the early stages of laminitis. |
Chronic Laminitis:
Laminitis is considered chronic after 48 hours of lameness or after rotation and/or sinking of the coffin bone (Fig. 5). Rotation (the more common phenomenon) results from the laminae at the front of the foot separating; sinking of the coffin bone below the coronet band is from the letting go of the entire laminar junction. It is important that radiographs be taken to determine the actual position of the bone. Either or both of these changes to the position of the coffin bone may be mild or severe, even to penetration of the coffin bone through the sole of the foot.
Causes of Laminitis:
The exact cause of laminitis is unknown. Occasionally, laminitis will develop for no apparent reason. However, usually laminitis develops as a sequel to a systemic disease or condition. Numerous predisposing factors have been identified. They can be divided into five major groups:
- carbohydrate overload: excess grain, lush pasture, sudden feed change
- endotoxemia, sepsis, shock: colitis, intestinal obstruction, pleuritis, retained placenta, metritis, abortion
- excessive unilateral weight bearing: post-fracture repair, severe lameness
- management: black walnut bedding, cold water ingestion by overheated horse, overweight animal, unconditioned animals worked on a hard surface
- miscellaneous: corticosteroid treatment, Cushing disease, hypothyroidism
Therapy:
The treatment of horses that develop acute laminitis should be considered an emergency. It is imperative that the underlying primary disease is identified and treated as soon as possible by your Veterinarian. A delay of even a few hours can make the difference between a successful outcome and a failure. If any of the known risk factors for laminitis have occurred, therapy should be started before the clinical signs become visible. The treatment should be focused on elimination of the cause or triggering factor, blocking the pain, prevention of any further disruption of the attachment of the coffin bone to the hoof wall, promotion of healing, and maintenance of the systemic health of the horse. Until your Veterinarian arrives, the horse should be moved as little as possible and be encouraged to lie down by adding deep bedding to its stall if indoors. Don't feed anything to your horse nor administer any drugs unless advised to do so by the Veterinarian.
Most of the recommended therapeutic regimens have value, but no one procedure has been shown to be superior to any other. If the laminitis progresses to the chronic stage, teamwork among you, your Veterinarian, and your farrier will become necessary for the best possible outcome for your horse. There will have to be a plan instituted involving dietary, medical, and therapeutic trimming and shoeing options. The time and cost may be prohibitive and a high level of dedication necessary and still the prognosis will be uncertain. In cases of acute laminitis, it will take at least eight weeks before any prognosis can be given; in chronic cases it can take from four months to a year before the future performance abilities can be estimated. Horses with more than 15 degrees of rotation accompanied by downward displacement of the coffin bone into the hoof capsule within four to six weeks of the initial episode of laminitis have a poor prognosis. Considering the enormous pain for the horse, it seems not humane to treat a horse with prolapse of the coffin bone through the sole. In protracted and/or severe cases of laminitis, euthanasia should be considered.
Diagrams: Janet Douglas, PhD.
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