Feeding a low sugar, high fibre diet is correct, but why?
The problem is not sugar. Fibre is made up of sugar. Sugars are converted to glucose, the single most important energy provider in any species. Fibre is fermented in the hindgut, generating volatile fatty acids (VFA) one of which (Propionic) is converted to glucose in the body.
The problem is the amount. There is a limit to the sugars that can be broken down enzymatically and absorbed in the small intestine. Absorbed sugars are utilised immediately or laid down as storage. Those that are not absorbed pass into the hindgut.
The hindgut is populated with a range of different microbes, many of which can utilise the sugars in fibre. Fibre fermentation, producing VFA, maintains the neutrality of the hindgut providing an environment suitable for maintaining the optimal range of species for fibre fermentation. If the hindgut receives too much sugar, in any form, those bacteria that can utilise them will grow and flourish. As they do they create a micro-environment that encourages their growth at the expense of the “normal” population. Others that would not normally be established can exploit this new environment. Microbes that can utilise the end products of these bacteria can also begin to grow; the result is normal microflora balance is skewed and the environment becomes increasingly acidic, further pushing the balance in favour of the new populations.
Large amounts of starch set off laminitis by being fermented to lactic acid. Lactic is absorbed and only slowly metabolised to glucose in the liver. While circulating in the blood stream it causes a change in the pH of the blood and releases oxygenating free radicals at the extremities (where blood supply is limiting) causing inflammation. In the horse the predominant place is the lamella of the hooves. However there are other factors. High levels of protein entering the hindgut will, in an acidic environment, be fermented to nitrogenous compounds. It has been shown that some cause vaso-constriction, limiting blood removal, especially in the legs. This compounds problems caused by high lactate, reducing the flushing by fresh blood. Over-feeding a horse, supplying too much starch and protein, is a major cause of laminitis. It explains why spring grass, high in fructans and protein is such a problem; winter grass can be higher in fructans, if short cropped, but is not accompanied by high protein.
Therefore the rule in feeding the laminitic horse is to ensure the intake of starch and sugars is not too high, the same for protein. The protein requirement for activity is only marginally higher than maintenance, and feeding extra to an active horse is not advisable.
For starch, how much is over feeding? Recommendations, based on research, are that a normal horse should not eat more than 4 grams of starch (or total sugars) for each kilogram of live weight, 2 for a laminitic. This equates approximately to a ration of 10% starch and sugars.
It is possible to choose feeds that are low in starch, low in protein and high in fibre. But this can be a hidden danger. The profile of the fibre is also important.
Fibre is the term for carbohydrates that have a different bonding to starch, sucrose etc. These bonds are only broken by hindgut bacteria. Although most end products are the VFA, there are others, including lactic and so knowing the relative profiles is useful. This is why fructans can be a problem. Too high a level, and incomplete fermentation will take place, resulting in a build up of glucose and fructose – and these can fuel those bacteria that lead to population change and the wrong hindgut environment.
Feeding the laminitic isn’t complicated and can be achieved if the above is borne in mind, leading to a few simple rules: