The pedal bone in the horse’s foot is covered by sensitive laminae which interdigitate with the non-sensitive laminae lining the hoof capsule. This anatomical arrangement normally maintains the stability of the pedal bone within the foot. Laminitis literally means inflammation of the sensitive laminae which can lead to rotation or sinking of the pedal bone, and is clearly a very serious condition.
The cause of the lamina damage is essentially due to oxygen deprivation or hypoxia.
This occurs due to blood being shunted away from the capillaries that supply the laminae and straight into the venous system. Changes in blood pressure and increased permeability of the blood vessel walls leads to fluid seeping out into the surrounding tissues causing oedema. The blood vessels within the hoof seem to be very sensitive to substances which cause vasoconstriction and this is the root cause of the condition.
The scientific world is at loggerheads trying to decide exactly which enzymes, chemical mediators or toxins are responsible for causing all these vascular changes. If we were sure, then drug therapies could be more specifically targeted to block their action. What we do know for sure are the clinical situations that lead to laminitis:
- Carbohydrate overload i.e. horse breaking into the feed room and eating a bag of oats.
- Absorption of bacterial toxins from a retained placenta for example or from a severe colic.
- Equine metabolic syndrome including obesity and insulin resistance.
- Cushings syndrome.
- Ingestion of high levels of fructans in grass.
- Trauma such as from shoeing can lead to laminitis but usually there is some other predisposing cause in conjunction.
- Over usage of corticosteroids can lead to vasoconstriction of the digital vessels and severe laminitis.
Therapy for the laminitic is aimed at stabilising the foot, then removing or treating the underlying cause. Correct management of the foot is critical for determining the outcome of the case. Placing the horse on strict box rest on a deep bed of clean shavings is the first step. Radiographs will be required to assess pedal bone position and to identify pockets of gas or fluid which may be exerting excruciating pressure within the hoof. If found, they must be vented quickly, usually through the dorsal hoof wall via a dorsal wall resection. The pedal bone will need supporting to prevent further movement and this is best achieved using a glue-on plastic heart-bar shoe. Pain relief and anti-inflammatory therapy is usually provided using phenylbutazone. In extreme cases it may be necessary to apply fentanyl patches or to administer pain relief via the epidural route.
Foot recovery is slow following a major laminitic attack and the overall result depends largely on the integrity of the blood supply. With solar penetration that accompanies severe rotation, many of our patients take 12 months to grow a new hoof. It is important to remember that laminitis can affect all four feet, not just the fronts. Increase in the “throbbing” of the digital pulses in the feet is a good parameter to monitor in the laminitic during recovery and indeed can be an early sign that your horse is suffering from this dreadful condition.
The outcome of these severe laminitic cases is reliant on the vet and farrier working closely together to make the correct foot management decisions. Any change in the comfort levels must be reported to us immediately as it is common to get pockets of infection which need to be released as soon as possible.