The bone within the hoof is called the coffin bone (or P3). It is attached to the hoof capsule via thousands of interdigiting leaf-like lamellae (laminae). When inflammation of these connective tissue structures or laminae occur it is called laminitis (founder is a layman’s term for laminitis). When this inflammation occurs, the tight interdigiting connections between the laminae start to break down and the coffin bone begins to rotate or sink within the hoof capsule. When there is inflammation/movement of the coffin bone the horse demonstrates pain, usually within both front feet and sometimes all four feet.
Clinical signs of pain include reluctance to move, frequently laying down, walking tenderly on both front feet (appearing as if they are walking on egg-shells), increased heat of the feet with throbbing digital pulses. They often have a classic stance where the horse puts both front limbs out in front (camped out). The categories of laminitis are acute (a new/recent episode) or chronic (a continuation of the acute stage that begins at the first sign of rotation/sinking of the coffin bone). The acute category can be subdivided into mild, severe, and refractory (unresponsive). The chronic category can be subdivided into early chronic, chronic active, and chronic stable.
Predisposing factors and causes of laminitis can be numerous. Some of which include grain overload, infections within other areas of the body, obesity, insulin resistance (Metabolic Syndrome), excessive lush pasture, Cushing’s disease, or excessive weight bearing on one limb caused by prolonged lameness of the other limb. Other causes of laminitis can result from trimming the hooves too short, exercising on hard surfaces such as pavement and exposure to black walnut shavings.
Laminitis is diagnosed by clinical signs, radiographs of the feet, and nerve blocks that localize the lameness to the feet. Further diagnostic testing may need to be performed to determine the cause of the laminitis especially if an endocrine related cause is suspected such as Cushing’s Disease or Metabolic Syndrome.
If your horse is demonstrating signs of laminitis or has any of the predisposing factors listed above please contact your veterinarian.