Dr. Judith L. Mulholland

During the onset (FIRST), or developmental phase, lamellar separation is triggered and occurs before the symptoms of pain. This phase may last from 30 - 40 hours, depending upon the triggering factors. In some cases no developmental phase is recognised. Therefore, early symptoms may go unnoticed and the horse does not receive early treatment.

During the developmental phase, the horse may be suffering from some form of gastrointestinal, respiratory, reproductive, renal, endocrine or other organ system disease, and it is that disease process which leads to laminitis as a secondary condition. Treatment of the primary problem e.g., retained placenta, pneumonia, colic, grain overload, acidosis must be prompt and effective. Unfortunately, the feet may not be considered until laminitic symptoms appear. To wait and see if foot pain is the sequel to a metabolic crisis is to miss the most important opportunity to prevent or reduce laminitis.

During the developmental phase of laminitis, a period of vasodilation, characterised by increased hoof temperature, is strongly implicated. This can be treated by cooling the feet, which inhibits enzyme activity and decreases vasodilation. If you think that your horse or pony is developing laminitis, and the feet are warm with strong digital pulses. Bath the feet in ice and water now. Keep ice floating in the water at all times and continue this as often as practical e.g., 15 - 30 minutes every few hours for several days.

The laminitis, (SECOND), or acute phase is considered to be the first 48 hours after the symptoms of hoof pain are noticed. This phase lasts from onset of lameness, to downward displacement of the distal phalanx within the hoof. Not all horses go on to develop chronic changes in the hoof, and effective treatment and management of the primary cause and the laminitis itself at this stage can decrease the ongoing damage and long term effects.

The founder, (THIRD), or chronic stage, is when physical changes have occurred in the feet. The distal phalanx has sunk lower in the hoof capsule, caused by loss of the laminitic bond. The chronic phase can last indefinitely, with clinical signs ranging from persistent, mild lameness, severe foot pain, further degeneration of the lamellar attachments, hoof wall deformation, to extreme lameness, and in the most severe cases, penetration by prolapse of the distal phalanx through the sole or sloughing of the hooves leaving the distal phalanx exposed. This is a justification for euthanasia, however horses can survive this, (refer to sinker laminitis).

As the chronic phase progresses there is formation of the laminitic wedge, comprised of keratinised laminar/wall material, which further separates the sensitive and insensitive laminae. The distal phalanx is no longer able to align with the hoof wall normally and is described as rotated, or as I prefer to say “the pliable hoof capsule has been counter rotated away from the pedal bone by the formation of a laminitic wedge’.

The horse’s own body weight forces a degree of movement of the wall upwards over the pedal bone. This is described as sinking, but it is to be expected that if a tonne of horse is relying on the bonded laminae to suspend the sensitive hoof within the hoof capsule, and if most of these bonds were weakened or broken, the wall would simply slide up over the bone like a stone would sink in a glass of  water. It is an effect of gravity. This is why when this occurs to any degree, but especially when it occurs severely, that the horse is described as a sinker.