The equine gut microbiome
A microbiome is ‘all the microbes, their genomes and interactions in a particular environment' and the gut microbiome is a rapidly expanding area of research due to gene sequencing technology. The gut microbiome has an impact on:
Digestive health
Immune function (including allergies)
Obesity and insulin regulation
Cognitive function, anxiety and reactivity
What's normal and can it be tested?
Even just into the 2020s, its very early days in the research, so it's not yet known what is normal or ideal for the equine gut microbiome.
The idea that a horse's faeces (droppings) can be tested and interpretations made about the health status of that animal and furthermore, recommendations of feeding practices and supplements is very tempting for owners, but it is just not possible yet. Such a service is not based on scientific evidence.
The truth is that it is far too early to be able to accurately interpret equine gut microbiome information and there is no scientific evidence for the use of specific feed supplements to improve either gut heath or the health of the animal directly as a result of gut microbiome interpretation.
Professor Chris Proudman, a Royal Veterinary College Specialist in Equine Gastroenterology stated (in 2019) that ‘there is huge variation in the normal equine gut microbiome' and the understanding of equine gut microbiome that could lead to possible health benefits and disease prevention will only be possible if large amounts of funding are supplied to scientific research in this area.
He's not the only expert to publish such views. A German team recently (2019) published a review paper in which they stated ‘current gaps of knowledge hinder adequate progress with disease prevention and microbiome-based interventions'. They also state that ‘disturbance of gut microbiota leading to or indicating illness still needs to be defined (for horses)'.
It is too early to offer an accurate equine gut microbiome analysis and accompanying specific diet recommendation service.
More details about gut microbiome knowledge to date
There is some understanding of the main microbial populations in the equine gut, but it is general and non-specific. It's possible that a standard gut microbiome may not exist and there may be normal individual differences. Furthermore, fluctuations in the gut microbiome are normal, and this has been shown in research of pasture-kept, winter-haylage-fed horses over a 12-month period (e.g. Fibrobacteres varied from 3.45% to 23%). The gut microbiome in pasture-kept horses altered with forage provision, season and weather conditions.
The use of faeces to investigate the gut microbiome has its own limitations. Faecal microbe testing does not reflect the microbiome of the stomach, small intestine or caecum – only of the colon and even then, not exactly (the microbes in the faeces might not be exactly the same as what is retained in the colon).
How to keep the gut microbiome healthy and happy
Care should be taken with trying to manipulate gut bacteria without adequate understanding. For example, Fibrobacter bacteria are fibre-degraders so they might seem to be beneficial, but research has shown that obese animals seem to have increased proportions of these bacteria.
It's tempting to feed a supplement to try and manipulate the gut microbiome, but it doesn't make any sense to recommend specific feeds in small amounts, or specific feed supplements without considering the majority of the diet. For example, if a horse has variable forage intake like pasture grass one day and only hay the next, this is likely to have a much bigger impact on the gut microbiome than adding a handful of alfalfa, or a herbal supplement.
Probiotic and prebiotic supplements do have an impact on gut health however, with some evidence available to support this. Live yeast, deactivated yeast and polysaccharides FOS (fructo-oligosaccharides) and MOS (mannan-oligosaccharides) are amongst pro- and prebiotics available for horses. Unfortunately, in 2024, live bacteria are not authorised as legal for use in horse feed supplements in the UK or the EU.
At the current time, the best strategies to keep the equine gut microbiome healthy and happy include:
Make all dietary changes gradually (the most important by far)
Ensure a high fibre diet (with some highly fermentable fibre)
Maintain some diet diversity
Don't over-feed NSC (grass fructan, sugar, starch)
Avoid too much harmful stress
Avoid antibiotics unless necessary
Feed probiotics and prebiotics during periods of potential gut disturbance e.g. antiobiotics, deworming medication, stress, travel, change of diet