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If you regularly feed your horse carrots, apples, or beet pulp (including unmolassed) in winter, you ensure slowly but surely the growth of micro-organisms in the large intestines, a population that utilises pectins (plant building material from fruit, vegetables, and young grass/leaves) to multiply.

This does not sound problematic at first, as the horse is dependent on a functioning microbiome in the large intestine in order to obtain energy from plant fibres. The problem lies rather in the fact that in the natural diet of the steppe animal horse, pectins are only available during a very short growth period (namely after the winter rains) and only in small quantities. The main food source for horses in evolution has always been other plant fibres, essentially cellulose and hemicellulose.

The pectin-degrading microorganisms are therefore actually always present in the horse’s large intestine, but only in very small quantities. And that’s a good thing, as they prefer an acidic environment and usually set pH values around 5. The cellulose-degrading microorganisms, i.e. the actual microbiome of the horse, require pH values in the neutral range around 7.

In wild horses, the pectin-degrading fraction can therefore only multiply for a brief moment, namely when the steppe turns green for a few weeks after rainfall.

Then the plants dry up due to lack of water and for the next 9-10 months there is only cellulose again, so that this fraction declines and is again displaced by the cellulose-degrading microorganisms. However, if pectin-containing feed is fed diligently throughout the winter, then this fraction is fed in a targeted manner.

As soon as such a horse comes onto the pasture grass, a lot of pectin reaches the large intestine via the young spring grass in a very short time. The well-prepared pectin-degrading fraction can therefore multiply abruptly, which leads to a rapid reduction in the pH value and thus to a mass death of microorganisms in the large intestine that cannot cope with the acidic pH values. They dissolve in the intestinal tract and release their substances, known as endotoxins, which can be absorbed through the intestinal wall. If large quantities of endotoxins enter the bloodstream, they can trigger laminitis.

Fructan can trigger laminitis via a similar mechanism, but other microorganisms are involved here, mainly lactic acid bacteria, such as those that enter the large intestine through the regular feeding of haylage, brewer’s yeast or products containing lactic acid bacteria.

If the horse ingests large quantities of fructan in this case (e.g. in spring on warm, sunny days and cold nights), the fructan reaches the large intestine and the lactic acid bacteria can multiply excessively here.

The lactic acid they produce acidifies the intestinal environment very quickly, which can also lead to endotoxic laminitis. Of course, the plant composition of the pasture always plays a role here. I can also graze horses with dysbiosis (incorrect fermentation, shifts in the microbial environment of the large intestine) in a relatively relaxed manner on a lean grass pasture that resembles a steppe in terms of vegetation, as it is predominantly covered with herbaceous plants and lean grasses that only have a low pectin content.

But if my pasture is a beautiful, leafy, green meadow, then I should be more careful, because there is a lot of pectin in the leaves and on most pastures, we now have a high covering of performance grasses, which form much higher fructan contents than lean grasses.

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