Laminitis is described as a multifactorial disease as no single trigger is entirely responsible for causing the condition. Likewise, a simple solution does not exist as a combination of factors needs to be considered. Many researchers are studying the disease by looking at the anatomy, diet, grazing and metabolism of glucose and insulin and it is hoped that eventually their findings will slot together so that we have a better understanding of its aetiology, and can develop practical methods for its prevention.
Laminitis is most commonly caused by incorrect diet, usually from excessive consumption of sugars and starch in either hard feed, or most commonly grass particularly during spring and autumn when there are flushes in grass growth.
It is triggered by a chain of events which start in the gut and lead to a metabolic dysfunction which reveals itself in the feet. As the cause is frequently dietary, and the horse’s digestive system is his first line of defence, it is possible to make adjustments to the horse’s feeding regime that will encourage a healthy gut and increase his chances of combating the condition more effectively.
In this article we will look at some of the feed ingredients which are currently being studied in the hope that they may be of benefit to laminitics. It must be appreciated that no herb or supplement is going to be a ‘magic bullet’ as laminitis is such a complex condition; but it is hoped that correct nutrition along with veterinary care, exercise and good management will go someway to improving the quality of life for our horses.
Antioxidants are molecules capable of slowing or preventing the oxidation of other molecules. Oxidation reactions produce free radicals which start chain reactions that damage cells. Free radicals are produced naturally in the system as a result of everyday life such as exercise or aging, but when there is excessive production the likelihood and severity of illness or disease will increase.
When blood circulation is restricted, such as in the hooves during laminitis, the production of free radicals is thought to increase and this can cause significant damage both locally within the laminae and systemically. Trauma and inflammation which also occur during laminitis have also been implicated in the production of free radicals. A recent study (Neville & Hollands 2004) showed that chronic laminitics may have three times the amount of free radical damage when compared to non-laminitic ponies, even when they had not shown signs of the disease for some 24 months. The body protects itself from free-radical damage with anti-oxidants that stabilise the free radicals so that they can no longer cause damage. Antioxidants are produced naturally by the body but during times of stress it may be necessary to supply an additional source in the diet.
Horses and ponies suffering from chronic laminitis are often maintained on restricted grazing and a limited diet. However as fresh grass is the major source of antioxidants for horses this can have a counterproductive effect. It is therefore advisable to include a supplementary source of antioxidants in the diet of horses on restricted grazing, and particularly those who have suffered from laminitis who may have increased levels of circulating free radicals. Antioxidants for horses are often provided in the diet in the form of trace elements such as selenium, zinc & manganese, vitamins such as vitamin C and vitamin E and plants with high levels of antioxidants (particularly the spices). Anti-oxidants are not a cure for laminitis but research recommends their inclusion in the diet.
Recent research has shown a link between insulin resistance and laminitis (equine metabolic syndrome). This appears to be most likely in certain breeds of horse, such as the native breeds which are genetically adapted to live off sparse vegetation. Domesticated natives are likely to be kept on pastures much richer than they were designed to eat, and are therefore more sensitive to the sugar content than other breeds. A combination of too little exercise and a diet high in soluble carbohydrates (grass sugars) can predispose a horse to insulin resistance, and a cresty neck with fat deposits over the rump and above the eyes may result. If the body loses its sensitivity to insulin, it will not be able to produce enough to trigger the transfer of glucose from the blood into the cells, resulting in starvation and damage of the cells. It has been suggested that the provision of additional magnesium in the diet may help manage the insulin resistant horse. Magnesium affects both insulin secretion and action and therefore plays an essential role in glucose balance. Low intracellular magnesium levels may result in impaired insulin function. In general, forage in the UK provides adequate magnesium, but grass analysis has shown a huge amount of variation between crops and seasons and it is well known that spring grass is often deficient. As magnesium competes with calcium for absorption sites in the gut, a high calcium diet will also reduce the amount of magnesium that can be absorbed. It is therefore good advice to ensure that the laminitic pony receives adequate levels of all vitamins and minerals, and importantly magnesium.
Like magnesium, cinnamon is also believed to help the cells to respond to insulin. A compound found in cinnamon known as MHCP (methylhydroxy chalcone polymer) is thought to inhibit enzymes that block the insulin response procedure. So far the only studies have been carried out on humans but research has shown that cinnamon can significantly reduce blood sugar levels in people with type-2 diabetes (a condition linked to equine metabolic syndrome of horses which is caused by insulin resistance). In the trial, 60 people with type-2 diabetes were given either cinnamon or a placebo. After 40 days those eating cinnamon showed reduced fasting levels of serum glucose by as much as 29% (Khan et al 2003). Extracts of cinnamon have also been shown to act as powerful antioxidants, which could lead to additional health benefits for the laminitic horse.
The trigger factors linking the gastro-intestinal tract with the onset of laminitis are complicated and not known precisely. However, we do know that excess carbohydrate reaching the caecum in the form of starch or water soluble fructans will result in the fermentation of bacteria that produce lactic acid (lactobacilli and streptococci), and that this occurs at the onset of laminitis (Garner et al 1978) (Medina et al 2002). One theory links the increase in lactic acid (and therefore decrease in pH) with the death of the healthy bacteria resulting in the release of endotoxins into the blood stream. It is believed that these endotoxins may be responsible for the vasoconstriction of blood to the hooves. An alternative theory is that the production of amines as a result of fermentation may be to blame. As lactic acid is produced and the pH drops, the permeability of the caecal mucosa increases so that potentially damaging amines can be more freely absorbed.
The effect of live yeast (saccharomyces cerevisiae) on the equine digestive system has been thoroughly researched and with our understanding of lactic acid production and laminitis, live yeast should be recommended for its positive effects on digestive balance. When live yeast is fed, the effect of excess starch consumption and acidosis on the microflora of the gut will be reduced, therefore helping to keep the gut stable. (Moore & Newman 1994) Without yeast, a high starch diet could lead to four times more lactic acid in the caecum than a high fibre diet. The same diet with yeast showed almost normal pH values in the hind gut (Medina et al 2002). With this understanding of the link between digestive stability and laminitis, live yeast could be recommended for its positive effects on digestive balance. Live yeast reduces the build up of lactic acid by helping to consume the excess glucose in the gut, and it will also help to mop up oxygen which is toxic to the beneficial microflora.
Our understanding of laminitis and how to manage it is improving all the time as a result of the extensive research being carried out with the collaboration of veterinarians and nutritionists across the globe. Currently, at the Royal (Dick) School of Veterinary Studies, The Horse Trust is funding a project studying the effects of mint derivatives in relation to the pain of laminitis. As many laminitics have to be humanely destroyed as a result of the pain rather than the condition itself, the discovery of an effective pain reliever would be a fantastic result. As the pain is neuropathic the usual anti-inflammatory drugs are ineffective. In years to come, the combination of weight control, pasture management, regular exercise and targeted nutrition should see laminitis as an easily preventable condition for most horses.