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All sugars used in feed, whether in roughage, concentrates or supplements, come from natural sources. Sugar is produced in plants in a process called photosynthesis. The energy contained in sunlight is bound in the form of chemical energy. In addition to the green leaf pigment chlorophyll, the plant also needs carbon dioxide (CO2) and water (H2O). The carbon atoms of CO2 are chained together with the help of solar energy and formed into a ring, the ends of which are saturated with oxygen (O) and hydrogen (H). What remains is oxygen, which is released into the atmosphere as O2. This process produces different forms of sugar: fructose (fruit sugar), glucose (dextrose, grape sugar) or sucrose (disaccharide). The plant can then build polymers from these sugar building blocks. These include structural carbohydrates such as pectin, cellulose, hemicellulose and lignin, which it needs for growth. But storage carbohydrates are also formed from it, such as the short-term store fructan or the long-term store starch. In digestion, a distinction is made in horses between sugars (do not have to be digested, can be absorbed immediately via the mucous membrane of the small intestine) and starch (must be enzymatically broken down into sugar in the small intestine, is then absorbed via the mucous membrane of the small intestine) and structural carbohydrates (are fermented by microorganisms in the large intestine, whereby mainly propionate, butyrate and acetate are formed, which are absorbed via the mucous membrane of the large intestine).

The difference between carbohydrates digestible in the small intestine and those digestible in the large intestine is essentially their different effect on blood glucose levels.

Sugars contained in plants or molasses and the sugar obtained from starch in the small intestine are absorbed directly via the mucous membrane of the small intestine and enter the blood as sugar – thus causing the blood sugar level to rise. The energy sources from structural carbohydrates (propionate, butyrate, acetate) have no direct influence on the blood sugar level. Propionate can be converted into glucose by the liver when the blood sugar level drops, e.g. during physical work. However, this mechanism is rarely utilised; instead, the horse is able to use these derivatives directly in the cells as an energy supplier.

The source of the sugar is completely irrelevant for the body. The sugar in molasses comes from sugar beet, so it is also of direct plant origin. It is produced in the leaves of the beet and stored in the root as a reservoir to be available for the plant to sprout the following year – provided it is not harvested and processed by humans. The sugar from the sugar beet or from the waste product of white sugar production, molasses, is absorbed directly in the first third of the small intestine, as is the sugar content that comes from hay or grass.

The sugar content of roughage varies considerably depending on the vegetation on the land. Horses are naturally adapted to very low sugar levels in their forage. Steppe grasses generally contain <4% sugar, so that wild horses are essentially dependent on energy from structural carbohydrates. However, due to the modification of our meadow grasses through targeted seed breeding, we are finding more and more so-called high-sugar grasses on pastures and in hay, which have been produced for performance farming (dairy and fattening cattle) and for optimised ensiling. Ryegrass can have a sugar content of up to 36%! Unfortunately, the seeds of such high-sugar grasses do not remain in the areas where they were originally sown, so they continue to spread. As they are also very stress-resistant and assertive, they can continue to displace desirable, horse-friendly low sugar grasses on hay meadows and pastures. The average sugar content in hay has been rising steadily for years. It would be desirable for horses to have a sugar content of <10% in their hay (<6% for good doers and metabolism-sensitive horses). However, reality shows that most hay samples (late first cut) tend to have a sugar content of 12-14%. If you find one with 10%, then you are excited about this ‘low sugar’ hay. This means that with 1kg of hay, the horse ingests 120 – 140g of sugar. If you extrapolate this to a daily ration and assume that the horse gets 10kg of hay (500kg horse, 2kg hay per 100kg body weight), then we are talking about 1,200 – 1,400g of sugar that is absorbed in 24 hours. For comparison: a packet of household sugar contains 1,000g.

Horses eating mineral feed
© Adobe Stock/Annalene

If 2% molasses is added to the mineral feed and the horse consumes a daily dose of 100g, that is 2g of sugar. For comparison above: a sugar cube has 3g. We are therefore talking about quantities between 1 sugar cube (molasses from mineral feed) or 1.5 packets of sugar (from hay). Physiologically, the processing of sugar from molasses and sugar from hay is exactly the same – the sugar absorbed in the small intestine must be filtered out of the blood and temporarily stored in the muscles and liver. Ideally, it is then utilised in the muscles through work, if not, then – depending on the breed predisposition – there is an unclean breakdown and storage in the connective tissue (lymphatic retention, pseudo-EMS) or a build-up of fat reserves (EMS). It therefore depends less on the source of the sugar and more on the amount that enters the bloodstream per unit of time.

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