Laminitis is a disorder that is associated with overfeeding sugar or water-soluble carbohydrates. It is not a disease, rather the result of several conditions. It is very specific; an inflammation and, ultimately, breakdown of the lamellar (connective tissue) holding the hoof to the bone of the toe. There are three phases – developmental, acute and long term chronic.
Obviously the condition is painful, leading to the horse adjusting its stance to alleviate discomfort, which gives the distinctive pose, and also gives rise to abnormal hoof growth.
The actual physiology of laminitis at hoof level involves poor circulation, vasoconstriction and pooling of toxins (from disrupted hindgut fermentation), pro-inflammatory factors, oxygen starvation and the inability of glucose to energise normal hoof metabolism. The major instigators of these factors are endocrinological – obesity, insulin resistance PPID, dietary (too much fructans, sugars, overeating), or mechanical (bruising, wounds). Finally, breed is a factor, with our native breeds being most susceptible. Individually, these causative factors may not trigger laminitis, or just give mild symptoms, but a combination of different aspects can increase the risk and severity. For example, an obese horse on a high starch diet will be more liable to laminitis than a lean animal on a high forage diet. And mechanically, a heavily obese horse with hoof damage can exhibit laminitis where a lighter horse would not.
So, how can we reduce the risk of laminitis? There are two main routes; physical and nutritional. Physically, checking hooves for punctures or bruising is an easy task; obviously, but possibly overlooked, is exercise. Regular and continuous exercise helps circulation and keeps the lamellar oxygenated and flushes away pro-inflammatory factors and toxins. Equally important is weight control; an overweight horse puts extra stress on the hoof.
Bearing in mind the physical impact of obesity, there are also physiological problems. Fat deposits produce inflammatory markers and interact with insulin production. Insulin has a direct effect on the strength of the lamellar, so reducing insulin production is a positive thing. This also links in with IR, PPID and PSSM – disorders involving carbohydrate dysfunction. And this leads into nutritional regimes to support a beneficial diet.
Overfeeding has two outcomes. Absorbing large amounts of sugars (both directly and from digested starch) is accompanied by rising levels of insulin which impacts directly on hooves, but also, through IR, can result in hyperglycemia, which is a factor. If too much is fed, excess sugars and protein can enter the hindgut and upset the microbial population. Fermentation products change and bacterial toxins rise; lactate increases gut permeability and toxins, vasoconstrictors and oxidative molecules are absorbed; all of these are negative components in laminitis. If high levels of fructans (the soluble carbohydrate in spring grass) are fed, the end products further allow malabsorption, leading to laminitis.
So, to maintain a horse on a route that does not lead to laminitis, regular hoof checks, exercise and a diet low in sugars, water soluble carbohydrates and protein will ensure good absorptive function, hindgut integrity and reduction in the negative factors that cause damage.