Laminitis by Max Hannan BVMS MRCVS What is laminitis?
Laminitis is the inflammation of the lamellae, the microscopic ‘fingers’ of membrane that hold the pedal bone to the hoof capsule. These fingers of membrane clasp one another tightly, a bit like Velcro, ensuring the bone and the hoof work together as one. When the lamellae become inflamed two key things happen: firstly, they swell within the confined space of the hoof which is painful as the tissue cannot expand; secondly, the fingers lose their tight grip on one another, allowing the pedal bone to move within the hoof capsule.
condition known as insulin resistance, part of the overall condition known as equine metabolic syndrome (EMS). It can be helpful to think of it as similar to type 2 diabetes in humans, although it does not have the exact same underlying mechanisms.
Mechanical causes of laminitis are much less common than endocrine causes, but do happen. For example, high concussive forces on the feet from working on hard surfaces have been reported to cause laminitis. Excess weightbearing on one limb can also put enough strain through the foot to cause laminitis, such as if a horse is recovering from a broken leg and putting all his weight through the sound limb.
Finally, laminitis can occur aſter a horse or pony has been seriously unwell with blood poisoning, what we call toxaemia. The bacterial toxins from the disease enter the blood stream and cause damage all around the body, including to the lamellae of the hoof.
Diagnosis
What causes laminitis
While the exact mechanisms underlying laminitis are still being understood, we know that broadly speaking laminitis is caused by endocrine factors (hormones), mechanical factors (external forces on the hoof), and certain systemic diseases such as toxaemia (blood poisoning).
Endocrine laminitis is the most common cause of laminitis in the UK. The two primary hormones responsible for laminitis are cortisol (a stress hormone) and insulin (the hormone that helps metabolise sugar). Cortisol is over-produced in horses suffering from PPID (Cushing’s disease), in normal concentrations the hormone is important for all sorts of bodily functions, but too much cortisol can damage the lamellae as well as lowering immune function generally. Even a horse that doesn’t look like it has PPID might have enough excess cortisol circulating to damage the lamellae causing laminitis. The second hormone, insulin, is released whenever horses (or humans!) eat a meal high in starch and sugar. Grains, haylage and growing grass typically contain high levels of starches and sugars, and in response the body releases insulin which helps store sugars within cells, aſter which the insulin level returns to a normal low level. Horses, especially our natives and ponies, are simply not evolved to eat such high levels of starches and sugars all year round. In response, their bodies constantly release insulin which leads to a
14 THE SPRING SPECIAL 2020
While laminitis occurs all year round, spring time is the most common period for it to be diagnosed, when horses and ponies eat the new growing grass full of sugar. When horse owners think of laminitis, they think of the pony with that classic pottery gate and standing with the weight over the hindlimbs. However, the signs of laminitis can be very subtle, especially in the early stage. Any horse or pony can be affected by laminitis, although as discussed it is far more common in overweight individuals and those suffering from other conditions. While typically laminitis affects both front feet, it can be seen in just one foot, or all feet. Diagnosis is primarily made be clinical examination by a vet, including watching the horse move, checking the heat of the feet, the feel of the digital pulses as well as the sensitivity of the sole to hoof testers. Ideally this will be followed up by radiographs (x-rays) of the foot to assess the position of the pedal bone within the hoof capsule and the foot balance in general.
Treatment
While a diagnosis of laminitis might be overwhelming, the treatment is relatively straightforward and should be implemented and strictly
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