Digestive Aids for Horses Explained!

Article last updated: 24th October 2023

Just as you’ve got your head around the differences between probiotics and prebiotics, we now have ‘postbiotics’ to get to grips with! Recently defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP), postbiotics is the collective term for “a preparation of inanimate microorganisms and/or their components that confer a health benefit on the host”. This basically means that postbiotics, like prebiotics, are not live but unlike prebiotics, they are the end product of a process involving live bacteria or they are dead bacteria themselves.

What’s the difference between probiotics, prebiotics and postbiotics?

The term probiotic is often used to describe products that contain either bacteria or yeast (which is a fungus) because they are both ‘alive’ and have positive effects on the health of the gut. Currently, there are no bacteria probiotics approved for use in horses, so, if you are buying a product described as a probiotic, it is likely to contain live yeast.

Digestive AidWhat is it?How does it work?
ProbioticsLive bacteria - (none approved for horses)

Live yeast - most commonly Saccharomyces cerevisiae
In other species, probiotic supplements contain a range of bacteria known to be beneficial for health and digestion. Supplements literally top up numbers of beneficial species in the gut.

Fungi are part of the digestive process for breaking down fibre – they start breaking down the structure of the fibre allowing bacteria easier access. This makes the fibre digestion process more efficient so horses tend to get more from the fibre they are fed.
PrebioticsIngredients that have an effect on the bacteria in the digestive systemscFOS prebiotics are a food source for beneficial bacteria in the gut. Well fed bacteria will proliferate and out number pathogenic species – a process known as competitive exclusion.

MOS prebiotics attach to harmful bacteria and carry them out of the gut so they can’t become established.
PostbioticsInanimate microorganisms and/or the end products of microbial fermentation eg metabolites that confer a health benefit on the hostMetabolites from bacterial fermentation are found in the gut naturally and so adding more helps to counteract shortfalls particularly in animals on low fibre diets.

If inanimate or dead bacteria still retain their structure they are still ‘sensed’ by other micro-organisms in the gut who will react to them – a bit like ghosts might have an effect on someone who thinks they’ve see one!

There is more information on each of the different digestive aids below.

Why do we want to support bacteria in the horse’s gut?

Mammals produce digestive enzymes to break down certain nutrients such as carbohydrates and protein, but they can’t produce enzymes to break down fibre. Herbivores have evolved to rely on a population of micro-organisms, including bacteria, that are able to break down fibre for them. This process releases energy and nutrients from the fibre that the horse can utilise.

Various by-products are produced as a result of fibre digestion, including B vitamins such as biotin. The bacteria themselves are also an important part of the immune system, so help to maintain the overall health of the horse. The old adage ‘health comes from within’ really does apply, as poor-quality hooves, a dull coat and weight loss can all be related to an unhealthy digestive system.

Feeding live yeast to horses

Live yeasts are considered to be additives because they contain live micro-organisms and so should only be used in horse feeds if they are approved under UK/EU feed safety legislation. To gain approval, evidence supporting the effectiveness, safety and quality of the product has to be provided for different age groups of host animals eg foals through to veterans.

Feeding live yeast to horses has been shown to improve fibre digestion, which means that a horse should be able to get more energy from the fibre it eats. Fibre is a very complex structure and so the fungi in the digestive tract start the digestion process by prising apart the fibre’s structure – a bit like a parent cutting up a child’s food to make it easier for them to eat. If the structure is opened up to the bacteria they have a greater surface area to work on and they therefore continue to break down the bonds between the fibre molecules, fermenting the resulting sugar to produce volatile fatty acids such as acetic acid and butyric acid. Acetic acid is a major energy source for the horse both for maintenance and exercise and butyric acid is ultimately used as an energy source by the colonocytes (gut tissue cells).

The aim of trying to help the horse obtain more from the fibre it is consuming is to reduce the need for cereal based feeds, even for those working at harder intensities as there are so many benefits for health, behaviour and performance.

The use of prebiotics in horse feed

There are two types of prebiotic commonly used in horse feed – short-chain fructo-oligosaccharides (FOS prebiotic) and mannan-oligosaccharides (MOS prebiotic). ‘Oligosaccharides’ literally means a ‘few sugars’ and ‘fructo’ and ‘mannan’ indicates where the sugars come from, mannan referring to yeast, for example.

The bonds that join FOS prebiotics together can’t be broken down by the enzymes in the horse’s gut (just like fibre). Only certain types of beneficial bacteria in the digestive tract can break FOS down and utilise the energy to thrive and reproduce. By increasing their numbers, beneficial bacteria can keep harmful species at bay – a process known as competitive exclusion.

A study presented at the Equine Nutrition Conference in Hannover, in 2005, investigated the effects of FOS prebiotics in different parts of the digestive tract. The researchers found that horses supplemented with FOS had less acidic digestive tracts than those that weren’t supplemented and suggested that this could help to reduce the risk of problems such as gastric ulcers. Obviously, this research would need to be repeated before a definite claim could be made.

Mannan-oligosaccharides originate from yeast cell walls and, whereas FOS prebiotics are often referred to as a ‘lunch box’ for specific bacteria, MOS prebiotics act like sticky sponges that mop up pathogenic (harmful) bacteria such as E. coli and salmonella, and carry them out of the gut. If harmful bacteria can’t get established in the gut, the horse remains healthy.

Postbiotics for horses

In the loosest sense, any fermented food is a postbiotic and there has been some debate in human nutrition as to whether yoghurt, kefir and even beer can be described as postbiotics. Clearly these foods and drinks can be part of a healthy diet when consumed in moderation and will confer some positive effects on the consumer! In the context of horse and animal feed, ingredients defined as postbiotics need to be safe and consistently efficacious to be listed on the UK/EU feed materials register. They will be produced to very high standards taking into consideration the unique aspects of producing ingredients for horses such as ensuring they are safe for horses competing under FEI/BHA rules. This is why it is always recommended to use products specifically intended for horses.

Use of probiotics in horses

The use of probiotics in horses usually generates considerable debate because there has been little research specific to horses. Preliminary studies to identify the best bacteria to include in an equine probiotic were carried out a few years ago, but we are a long way from seeing the findings of these studies being developed and converted to finished products on the market. 

As a result other approaches have been taken including Faecal Transfer where faecal material taken from a donor horse that is known to be healthy, is administered to a horse that has evidence of dysbiosis or other chronic digestive tract issues. The belief is that by giving the horse microbes from the gut of a healthy horse, it will help to re-establish a healthy population of microbes in the recipient. In the absence of approved probiotics for horses, faecal transfer is trying to achieve a similar result. There have been positive outcomes in other species including humans but the process is in its infancy for horses. The transfer should be carried out by a vet and there is much debate about how frequently the process should be repeated and at what intervals. Please discuss with your vet if you are interested to learn more or feel it might be beneficial for your horse.

Using a digestive aid can be very beneficial for those with chronic issues or veterans who, as a result of age, are more vulnerable to digestive upsets. Travelling, competing and other causes of stress increase the risk of digestive health issues and so increase the case for using ingredients that can help to counter problems. However, none of the digestive aids will work efficiently if poor feeding practices aren’t corrected too so the first step should always be to ensure the basic rules of feeding are implemented as fully as possible. Click here to find out more about how to promote good digestive health.

If you have any queries about whether a digestive enhancing supplement might be of benefit to your horse, telephone the Dengie feedline on 01621 841188 or email [email protected].