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Laminitis – The What, Why and How you can help Prevent/Treat it with Soy Bean Hulls

Dr Mark Barnett (PhD), Owner & Equine Nutritionist for MTB Equine Services, Nutritional Consultant to Benchmark Horse Feeds.

For a long time now, laminitis has been thought to be a result of inflammation of the laminae of the hoof – the soft tissue structures that attaches the coffin bone of the foot to the hoof wall. Without the coffin bone properly attached to the inside of the hoof wall, the weight of the horse forces the bone away from the hoof capsule, damaging arteries and veins thereby restricting blood flow to the sole and coronet, causing extreme pain and lameness. The cause of this inflammation has thought to have been a result of an incidence of grain overload in the hindgut region resulting in acidosis and “leaky gut” syndrome or from systemic illness or infection such as a retained placenta in a mare. These certainly cause laminitis in horses but they only account for about 10 to 20% of all cases reported. The other 80 to 90% are a result of endocrinopathic (metabolic) causes, primarily insulin resistance (IR).

Endocrinopathic laminitis is a general term which describes laminitis that develops in horses with endocrine (hormonal) and/or metabolic disorders. This includes laminitis that is associated with obesity, IR and elevated adrenocorticotrophic (stress) hormone levels. Two common equine related diseases which are known to induce such symptoms are Equine Metabolic Syndrome (EMS), where a horse becomes obese amongst other things, and IR. Each one relates to an excessive intake of energy in the diet, particularly in the form of non-structural carbohydrates (NSC) – sugars and starch.

When a horse eats more than required for its performance level it stores the excess energy on the body as fat. This can lead to obesity. Fat deposits, also known as adipose tissue, are active endocrine organs that secrete reactive (e.g., leptin) and inflammatory (e.g., cytokine) hormones into the circulating blood system. When large amounts of these hormones are released, such as in the case of an obese horse, they can cause insulin resistance throughout the entire body of the horse. Obesity has increasingly been recognised as a welfare problem with its increased association with equine morbidity and mortality in recent years.

Insulin resistance (IR) is a failure of the body's organs and muscles to adequately respond to changes in the level of insulin in the blood because of a continual oversupply of sugar in the horse's diet. As a result, there is either an overload (compensated IR) or underproduction (uncompensated IR) of insulin in the blood meaning the animal is unable to regulate its blood glucose levels, similar to a human diabetic. Uncompensated IR is not common in horses but compensated IR is. Compensated IR is when the body notes an increase in blood glucose levels after eating and, although there is already a lot of insulin circulating in the blood, produces even more insulin to try and control blood glucose levels. When combined with a very slow insulin clearance or usage rate, the horse becomes hyperinsulinaemia (having excess amounts of insulin in the blood) which makes the condition even worse.

The link with these conditions is the excessive energy intake in the diet, particularly as sugar, causing elevated levels of insulin (hyperinsulinaemia) in the horse's blood. Why excessively high levels of insulin in the blood results in laminitis is still unclear but it is most likely due to an alteration in the blood vessel tone in the hoof resulting in a reduced or inconsistent blood supply. There is also evidence to suggest that elevated levels of insulin in the blood negatively affect the integrity of epidermal cells of the lamellar tissue causing a weakening of the attachment of the lamellae to the hoof wall resulting in laminitis. What is certain is that endocrinopathic laminitis is usually a non-inflammatory response and that most horses inflicted with the condition can have painful and non-painful bouts of laminitis for many years before it is noticed by the owner/rider and that, if the underlying metabolic disease remains unmanaged, recurrence of laminitis is likely.

So, excessive energy intake in the horse's diet (particularly sugars) leads to obesity and development of EMS and IR. Now that we know the underlying cause for endocrinopathic laminitis, how do we manage it to prevent reoccurring (chronic) laminitis? There are three components involved in managing the diseases – Diet modification, exercise and drug therapy with diet being the main method of minimising, even preventing, laminitis.

One of the common factors in all horses suffering from endocrinopathic laminitis is obesity. The first step is to reduce the horse's dietary calorie intake. Most horses will eat around 2% of their body weight (BW) in dry matter (DM) each day while ponies can consume as much as 5% each day. It's important to reduce the amount of energy they consume daily in their diet to induce weight loss while maintaining a balanced diet in all other nutritional aspects. This can be done by either feeding only 1.3 to 1.5% of their BW daily or feeding a diet that is much lower in energy content. If you are going to provide a less energy-dense feed, carefully consider palatability and digestibility. The lower the energy in the feed the more likely it is going to be less palatable and less digestible. Soaking of hay has been shown to effectively reduce water soluble carbohydrates (simple sugars) in hay but can also result in a loss of water soluble macrominerals like sodium, potassium, magnesium, calcium and phosphorous. Hay soaking can result in losses of up to 25% in DM. Chaff based diets can be an easy way to introduce a low NSC diet but they do potentiate the issues which come from limited chewing such as gastric ulcers, compaction and stereotypies.

There is another alternative – Soy bean hulls.

Soy bean hulls are a type of feed classified as Highly Fermentable (or Super) Fibres. Highly fermentable fibres are complex carbohydrates containing high levels of cellulose, hemicellulose, and pectin which can be readily fermented by the hindgut microbes, but contain much less of the non-digestible lignin than other fibre sources like hay and grass. They also contain high concentrations of readily degradable non-starch polysaccharides (complex chains of sugars that are not digested in the small intestine but can be fermented in the horse's hindgut but, unlike starch, are not used by microbes to produce lactic acid) that produce large volumes of Volatile Fatty Acids (VFA). These VFA are actually the primary source of energy for a horse, not sugars. Volatile fatty acids, primarily acetate, butyrate and propionate, are high-energy short-chain fats produced by microbes from fibre fermentation that travel safely through the blood (no insulin response unlike sugars) to be either converted in the liver to glucose or long-chain fats for storage or used as an immediate energy source. Fats, in fact, contain up to 3-times the energy density of sugars!

Soybean hulls are simply the seed coat of the soybean that have been removed from the bean during the oil extraction process. They are high in pectin as well as other soluble fibres including NSP, making them readily fermented by the microbes in the hindgut. Like other highly fermentable fibres they are low in sugars and starch meaning little risk of health issues such as acidosis and leaky gut syndrome and great for horses prone to laminitis and colic.

Studies have shown that most of the soybean hulls eaten by the horse are digested through microbial fermentation, meaning very little is wasted. Studies have also shown that the inclusion of soybean hull in a horse's diet greatly increases the amount of VFA produced, particularly propionate which favours the formation of glucose in the liver. In fact, soybean hulls were found to be so readily digested in the hindgut, producing such high quantities of VFA and increasing the population of the beneficial fibre-digesting microbes that it has been suggested they can replace up 75% of the total fibre in the diet and could be a suitable replacement for many grains and grain-based feeds used to traditionally increase the energy density of the feed.

In the past, to increase the concentration of energy in the horse's diet it was necessary to replace some of the low-energy hay with higher-energy, high sugar and starch grains. The introduction of highly fermentable fibres like soy bean hulls may be able to replace much of this grain in the diet as an alternative energy source. How much extra energy these fibres provide is unsure as the current measures of Digestible Energy (DE) are reasonably accurate for feed products like hay and grain-based feeds, but they may substantially underestimate the DE for highly fermentable feeds which contain over 35% crude fibre and a high concentration of NSP. This could mean that soy bean hulls may have a similar DE value as oats and barley, or even more, without the negative impacts seen from feeding large quantities of grain, like laminitis!