Laminitis and Founder
[What is laminitis?][Causes][Symptoms][Treatment][Aftercare/Prevention]
(Updated Apr 2008)
Structure of the hoof
The hoof is comprised of a hard outer wall and a sole underneath. Within this enclosing capsule are various sensitive structures, including the pedal (coffin) bone. Some 600 insensitive folds (laminae) of the inner surface of the hoof wall project in and mesh with an equivalent number of sensitive laminae (corium laminae) attached to the surface of the pedal bone. 100-150 secondary hoof wall laminae also bond with projections from the sensitive laminae. The result is that the pedal bone, which is the terminal bone of the whole leg, is totally suspended within the capsule of the hoof. The body weight and movements of the horse exert tremendous forces on this laminar suspension apparatus, but under normal conditions, sound hooves cope adequately with these pressures.
Research into exactly what happens at the cellular level is ongoing, but basically laminitis is a failure of the attachment between the sensitive and insensitive laminae, i.e. the laminar folds tear apart. Without their support, the pedal bone is driven down into the hoof capsule. Arteries and veins and other inner structures are torn and damaged. The pain is unrelenting and if not actually lying down, the horse adopts a shuffling gait and characteristic stance – the hindlegs are held well underneath in an effort to take the weight off the forefeet, which are extended forward. If laminitis is not treated or the treatment is unsuccessful, the pedal bone “sinks” (founders) and rotates downwards and this is known as founder.
The founder phase usually begins 48 hours after the first signs of pain and can continue for days or even weeks. It develops when a critical number of attachments between the laminae fail. In some cases the pedal bone rotates and sinks so far that it penetrates the sole of the hoof. Not all cases of laminitis lead to founder.
In some cases there is no obvious cause, but known triggers are −
Ingestion of large quantities of grain or lush green pasture (carbohydrate overload)
In association with or after recovery from an infection (retained placenta, respiratory illness, enteritis, colitis)
Following an episode of tie-up (recurrent exertional rhabdomyolysis)
Unfortunately the initial stages often go undetected. It is only once pain begins to manifest itself that it becomes obvious the horse has a problem. The first clinical sign is the shifting of weight from one foot to the other (paddling), usually forefeet initially. Prompt veterinary intervention at this stage may halt further lamellar damage.
The clinical signs then progress to one or all of the following −
Obviously sore feet, mostly front but sometimes rear as well. The toe region is very sensitive to hoof testers
Marked digital pulse, hooves feel hot
Short choppy strides, shuffling gait, reluctance to move, noticeable lameness, especially when turned tightly
Recovery to chronic laminitis phase −
A distinct depression can be felt at the top of the coronet as the pedal bone sinks down in the hoof capsule
Dropped sole − the sole changes from concave to convex
Laminitis is a medical emergency and if it is suspected, veterinary help should be sought immediately in an attempt to lessen the damage. The cause must be removed if known, e.g. prevent further access to grain or lush pasture. Most authorities believe that standing the horse in iced water, or even cold water hosing, helps reduce the pain and inflammation initially.
If an illness or disease triggered the attack, this must be treated first or concurrently along with the administration of pain relief and anti-inflammatory drugs, commonly NSAIDs e.g. phenylbutazone, which may be needed for an extended period of time. The application of a frog/sole support device can be invaluable in helping prevent the sinking of the pedal bone. In the case of grain engorgement, a mineral oil drench will aid removal of remaining grain from the gut and may block the absorption of toxins.
X-rays are taken at regular intervals to monitor movement of the pedal bone. The issue of exercise is controversial. Most authorities agree that the horse should be confined to a well-bedded stall until the acute phase has passed, then given light walking exercise. Under no circumstances should a horse obviously in pain and reluctant to move be forced to exercise.
Remedial shoeing is carried out once the acute phase is over. This is a specialist job requiring close collaboration between the vet and a competent farrier. Once the pedal bone has become stable, special shoes (e.g. heart bar) are applied which support the heels and frog and relieve pressure on the wall.
Laminitis causes crippling pain and the response to treatment can be unpredictable. In some cases euthanasia may be the most humane option.
Aftercare and preventing recurrence