Pre-, Pro-, and Postbiotics: Why Are They Important? | Equine Science Matters™

We often hear about prebiotics, probiotics and postbiotics, but what do these terms actually mean, and why are they important for your horse? 

Horses are hindgut fermenters, which means they rely on the caecum and large colon to break down the fibre in forage. Unlike humans, horses cannot digest fibre on their own. Instead, they depend on trillions of microscopic organisms living in the hindgut, collectively known as the gut microbiota. 

This complex community comprises bacteria, fungi, viruses, and other microbes that work together to ferment fibre. In doing so, they produce nutrients that provide much of the horse's daily energy requirements. 

But the gut microbiota does much more than simply digesting fibre. Research has shown it also plays important roles in immune function, controlling inflammation, maintaining the health of the gut lining, and communicating with the brain through what is known as the gut-brain axis. 

The challenge is that this microbial community is surprisingly sensitive. Changes in routine, travelling, competitions, stress, illness, dietary changes, and even switching to a new batch of hay can alter the balance of the microbes living in the hindgut. 

Prebiotics – Feeding the Beneficial Microbes 

Prebiotics are types of fibre that the horse cannot digest itself. Instead, they act as food for the beneficial microbes living in the hindgut. 

Different microbes prefer different types of fibre, so one of the hallmarks of a healthy gut microbiota is **diversity**. The greater the variety of plants and fibres in the diet, the greater the variety of microbes that can thrive. 

Providing a wide range of forage and fibre sources is therefore one of the simplest ways to support a healthy, hindgut ecosystem. 

Many digestive supplements also contain specific prebiotics, most commonly: 

• Fructooligosaccharides (FOS) 

• Mannanoligosaccharides (MOS)** 

These ingredients selectively nourish certain beneficial microbes involved in fibre fermentation, helping to support a balanced microbial population. 

Probiotics 

The World Health Organisation defines probiotics as “live microorganisms that, when fed in adequate amounts, provide a health benefit to the host”. 

In horses, the only probiotics currently approved for use are specific strains of the live yeast Saccharomyces cerevisiae. 

For probiotics to have any effect, they first must survive the acidic environment of the stomach before passing through the small intestine and reaching the hindgut alive. Once there, they can help support the activity of the horse's own fibre-digesting microbes. 

Research in humans and other species has shown that probiotics are highly strain-specific. Different microorganisms perform different functions, so one probiotic cannot be expected to do everything. A useful analogy using dog breeds; a Border Collie is an exceptional sheepdog, but you probably wouldn't choose one purely as a lap dog. Likewise, a Spaniel makes a wonderful family companion but isn't usually the first choice as a guard dog. Each breed of dog has its own strengths and purpose, and the same is true for probiotic microorganisms. Different microbial strains appear to perform different jobs. 

Research into the equine gut microbiota is advancing rapidly, but we are still learning exactly what the different microorganisms do in horses. Because horses have a very different digestive system and diet from humans, data from humans cannot be reliably extrapolated to horses. Certain probiotics that have a huge body of research behind their benefits for humans; they might not necessarily confer the same benefits to your horse. 

Postbiotics  

Postbiotics are the beneficial substances produced when the hindgut microbes ferment fibre. 

The most abundant postbiotics are volatile fatty acids (VFAs), which are absorbed through the wall of the hindgut into the bloodstream. They provide a slow, steady source of energy that is often described as "non-heating", making them particularly valuable for horses who are prone to stress or can be a little sharp. 

The three main VFAs are: 

•   Acetate – the most abundant VFA. It is used as an important source of energy by muscles and other tissues, and any excess can be stored as body fat. 
•  Propionate – transported to the liver, where it is converted into glucose through a process called gluconeogenesis, helping to maintain normal blood glucose levels and providing energy for high-intensity exercise. 
•  Butyrate is the preferred energy source for cells lining the large intestine. It helps maintain the health of the gut lining, supports the gut's protective barrier, and plays an important role in regulating inflammation. 

The production of these beneficial compounds depends on a healthy, stable hindgut microbiota. Sudden dietary changes, insufficient fibre, high levels of starch or sugars, stress and digestive upset can all disrupt the delicate balance of the microbiota and therefore fermentation, leading to a reduction in the production of these important postbiotics. 

The hindgut microbes also produce certain B vitamins and vitamin K, which contribute to normal health and metabolism. 

Another fascinating area of research is the gut-brain axis. The gut microbiota can influence the production of serotonin, one of the body's key signalling molecules involved in regulating intestinal movement and communication between the gut and the nervous system. 

Although around 90% of the body's serotonin is produced within the gut, it is important to remember that this serotonin cannot cross the blood-brain barrier and therefore does not directly influence mood or behaviour. However, there is growing evidence that the gut microbiota communicates with the brain through a variety of other pathways involving the nervous system, immune system and microbial metabolites. Exactly how these pathways interact in horses is still an active area of research. 

Both serotonin produced within the gut and butyrate also contribute to normal intestinal motility, helping keep digesta moving smoothly through the digestive tract. 

Ultimately, the healthiest hindgut is usually supported by the simplest principles: feeding plenty of forage, introducing dietary changes gradually, minimising unnecessary stress where possible, and maintaining a diverse fibre intake. These provide the ideal conditions for the hindgut microbiota to flourish and continue producing the compounds that help keep horses healthy.