Probiotics for horses

Professor Jo-Anne Murray
PhD, MSc, PgDip, BSc (Hons), BHSII, RNutr, PFHEA University of Glasgow Veterinary School


Probiotics and prebiotics are extensively used in equine feeding practices to modulate the balance and activities of the gastrointestinal microflora. Probiotics and prebiotics are commonly incorporated into horse diets, either as supplements or added to a commercial feed product. Probiotics are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. After antibiotics were banned in the European Union in 2006, alternative substances producing similar effects, such as probiotics and prebiotics were developed. Probiotics that are used in animal feeds include bacteria and yeasts; however, whilst probiotics containing bacteria have been used in other species and in research trials in horses, there are none currently registered for use in horses in the European Union (EU).


There are three yeast strains approved by the EU under the category of zootechnical additives and as part of a functional group of ‘digestibility enhancers’ for use in horses. Yeasts are single-celled micro-organisms that are part of the fungi kingdom. All of the yeasts that are registered are all strains of Saccharomyces cerevisiae.

Yeast supplementation in livestock nutrition has been commonly used as a growth promoter for many years as an alternative to antibiotics and antimicrobial drugs. There is a wealth of scientific evidence that Saccharomyces cerevisiae (S. cerevisiae) has positive effects on growth, performance, health and wellbeing, of livestock as well as helping to alleviate stress and enhance the immune system. Yeast is also used in horse nutrition, with a growing body of research reporting positive effects on gut health, digestion, performance, and behaviour.


In terms of digestion, yeast has been shown to have an important role in the microbial fermentation process in the hindgut of the horse. Yeast is a source of nutrients such as nucleotides, vitamins, organic acids, which are essential for bacterial growth. When incorporated into horse diets, the most common observation in yeast-related research studies is an increase in the fibre-digesting bacteria population and consequently fibre digestibility, mainly in fibre-rich diets. It is also thought that yeast uses oxygen from the gut environment making it more favourable for proliferation and activity of fibre degrading microbes that are known to require an anaerobic environment (no oxygen). Higher levels of fibro lytic bacteria make it more difficult for the less oxygen-sensitive lactic acid-producing bacteria to compete, thus lower levels of lactic acid are produced, and pH is maintained at higher levels.

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