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Inhalte Verbergen
1 The experiment
2 Where are the checks?
3 Alcohol in the horse intestines due to brewer’s yeast
4 Active or Inactive?
5 Conclusion
6 More on the topic

Brewer’s yeast for horses is currently the subject of extensive discussion on social media about an experiment conducted at the University of Halle (unpublished data: The letter with the results, written by the scientists conducting the experiment to the client, is available to Sanoanimal.de).

The experiment

In this experiment, the colon stimulation technique (COSITEC) was used to simulate digestion in the horse’s intestine under laboratory conditions and show that no ethanol is formed by the yeast when brewer’s yeast is added.

For this purpose, faecal samples from two different healthy horses were used in two runs each and incubated for 14 days with the constant addition of hay and starch to simulate normal intestinal transit. At the same time, dried (inactivated) brewer’s yeast from the manufacturer who commissioned the study was added. During this time, no ethanol formation by the yeast could be measured.

Where are the checks?

Certainly, a beautiful and, above all, complex experiment that shows that this brewer’s yeast did not produce alcohol under these conditions. However, the positive control, i.e. a non-inactivated brewer’s yeast that is capable of producing alcohol, is missing to show that the experimental setup is perfectly suitable for measuring the production of ethanol by yeast in the intestine.

Another option would have been to cultivate the inactive brewer’s yeast in the culture for 14 days and measure its growth every day. If it is indeed completely inactive, there would be no living yeast in this culture after 14 days and consequently it would not be able to produce alcohol or other substances in the horse’s intestine.

In other publications (1), alcohol production was nevertheless measured in autoclaved yeast (i.e. yeast treated with heat and pressure). Although the values were below 1%, the study shows that even this yeast was not completely inactive!

Furthermore, the extent to which the composition of the microbiome may change within the experimental setup was not investigated. Here, it would first have to be proven that the microbiome that originated from the horses remains stable throughout the “feeding” with hay and starch or in which direction it would shift and then stabilise.

The next step would have been to add brewer’s yeast and investigate whether the microbiome remains stable or changes, and if so, in what way it changes. Unfortunately, this level of investigation and checking for results is also completely missing.

Alteration of the microbiome with brewer’s yeast can have just as dramatic an effect on the horse’s health as the production of alcohol and therefore these results should not be missed off before recommending the feeding of such a product. (2,3).

Eating horses' mouths in the feed
A change in the microbiome caused by brewer’s yeast can
have dramatic effects on horse health
© Adobe Stock_Annalene

Alcohol in the horse intestines due to brewer’s yeast

The “autobrewery syndrome” to which this experiment alludes is also very rare in humans, otherwise all beer drinkers would probably be in permanent delirium. Other factors often play a role in affected people, such as type II diabetes / insulin resistance or other diseases that are already known to be influenced by an incorrect composition of the microbiome. The probability of measuring ethanol production by the yeast using the intestinal contents of a healthy horse in just 2×2 trials is therefore not very high.
Other test arrangements would have been much more suitable.

Active or Inactive?

The crucial point in this whole discussion, however, is how the horse owner can tell whether the yeast he has bought in good faith is actually no longer able to grow. And what happens in the horse’s microbiome if it is not 100% dead after all. Especially if the horse may already have dysbiosis (faulty fermentation) or pre-existing conditions such as insulin resistance.

This is because a living organism (in vivo) is still different from an in vitro experimental set-up, i.e. test models outside the body. The mucous membrane alone is missing, which could be important for colonisation with yeasts.
Just as with increased pectin feeding, a shift in the microbiome could well occur with brewer’s yeast feeding.
Even dead yeast cells can have an influence on the population of microorganisms in the large intestine. If they serve as nutrients for a type of microorganism that can multiply excessively due to the abundant food that is now available, this may lead to shifts in the overall population and can displace important symbionts.

And yet again, horses that are not in the best of health and already suffering from various metabolic disorders and illnesses are particularly affected: It is precisely these horse owners who then turn to brewer’s yeast in search of symptomatic relief. It is highly unlikely that there will be any improvements in the horse’s (intestinal) health.

Conclusion

Sanoanimal naturally welcomes the fact that more detailed studies are finally being carried out on the effects of brewer’s yeast feeding and its effect on the horses health.
However, there is still a long way to go and the subject needs to be analysed from various angles in well-designed studies with suitable control groups before it is possible to say for certain which brewer’s yeast is a suitable supplementary feed and in which scenarios it should be applied to benefit the horse.

More on the topic

If you would like to know more about feeding brewer’s yeast, you can read more here: Brewer’ Yeast for horses: is it beneficial?

Sources

Elke Malenke
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