Lizzie Drury MSc Registered Nutritionist

The horse evolved to be able to use grass and forages as a source of food and energy generation due to the presence of fibre digesting organisms in its gut. In order to digest these feedstuffs the horse needs to have a healthy hindgut, full of a stable microbial population. Feeding a diet that is based on these fibrous feeds is important to maintain a healthy hindgut but supplementing the ration with a live yeast can help to support this healthy environment, Daisy Good Grassoptimise the growth of the fibre digesting bacteria and help to reduce the incidence of hindgut acidosis.

Current Research

There has been much research conducted to study the microbial populations in the rumen but not a huge amount studying the populations in the equine ceacum. However, what data is available shows that many of the bacteria are genetically related to and carry out similar roles to their ruminant counterparts. If the balance of microbes is disrupted in any way this can have significant consequences on the health of the animal affecting both performance and well being. There is no doubt that the microbes are ESSENTIAL to the overall health of the horse and our main focus from a feeding perspective must start with considering the hindgut and keeping it healthy.

Anaerobic microbes have been isolated from the hindgut and these play an important role in supporting fibre digestion. These bacteria colonise the fibre particle and using their hyphae they start to pull the fibre particle apart allowing the colonization process to happen more quickly. In the event of hindgut acidosis or any drop in gut pH can reduce the activity and growth of these bacteria leading to a reduction in fibre digestion and utilization.

The ciliate protozoa tend to be more abundant in the colon and ceacum and are microscopically similar to those that are found in the rumen. Removal of protozoa from ponies fed either a high forage diet or a high concentrate diet had no adverse effect on feed breakdown, indicating that they are a non essential and other microorganisms can take their place. However, in the ruminant, certain species of protozoa have been shown to engulf starch particles and slow down the breakdown of starch, helping to regulate the pH of the rumen, while others play a significant role in fibre digestion. Removing these from the rumen can cause a 30% reduction in the breakdown of fibre, thus their role in the equine gut may actually be greater than was first thought.

Bacteria are found throughout the equine gut and are the most abundant type of microorganism. They display a wide range of different functions and are essential to effective digestion from the stomach all the way through to the hindgut. However, the largest numbers of cellulolytic bacteria are found in the ceacum.

Hindgut Acidosis

One of the most common causes of hindgut acidosis is starch overload, resulting in undigested starch reaching the hindgut. This leads to a rapid growth of amylolytic bacteria, which produce lactic acid during their growth. Lactic acid then starts to initiate a drop in pH, which then leads to a potential cascade of other events starting with the reduction of fibre digestion. As the pH continues to drop and other bacteria start to die the risk of illnesses such as colic significantly start to increase. Some of the dominant bacterial populations shift towards the Streptococcal species, which have been associated with the onset of laminitis.

Benefits of Live Yeast 

Live yeast can scavenge for oxygen and although the gut is considered anaerobic there are still some traces of oxygen. These traces of oxygen are supplementstoxic to the microflora and can come into the gut with the food or via gaseous exchange through the gut wall and bloodstream. As a result of improved anaerobicity microbial numbers are stimulated when animals are supplemented with live yeast. This supports optimum fibre digestion.

The fibre digesting organisms are particularly sensitive to pockets of oxygen as well as fluctuations in pH. Below a pH of 6 their effect is slowed and below a pH of 5.8 these organisms will start to die. As they start to die they lyse (break open) releasing toxins which can cross the gut wall and enter the blood stream causing an inflammatory response. This is associated with the onset of laminitis.

A live yeast will also compete with the Streptococci for sugars and overwhelm the numbers of Streptococci, hence helping to reduce their numbers.

Live yeasts also produce metabolites, which help to stimulate the growth of bacteria that utilise lactic acid hence helping to resist the drop in pH, which leads to hindgut acidosis. Some of these metabolites may also be used by the horse, especially the B complexes, which can improve hoof quality and growth and coat quality. More often the most visible improvement is seen in the consistency of the droppings.

The use of live yeasts can be particularly important for horses that are under an increased amount of stress, such as breeding or competing and travelling. Research has shown that there is a strong link between the gut and the brain, with cross talking occurring between the two organs via the nervous system. During periods of stress the microflora may change as a result of changes in motility etc, which can result in diarrhoea.

One study has shown that even a 2 hour journey can cause significant disruption of the microorganisms. The gut flora of these animals supplemented with live yeast also returned more quickly to the initial status quo that was observed prior to the transport stress. This supports the benefits of supplementing with live yeast.Haynet image

If we focus on maintaining a healthy hindgut and microbial population we also help to support the immune status of our horses. The more stable numbers of microbes that populate the hindgut the less of a chance there is that pathogenic bacteria can get a foothold and cause disease. The yeast acts like a piece of Velcro by sticking to the pathogenic bacteria and removing them from the gut, as well as helping to stimulate the gut secretions helping to reduce the likelihood of the pathogens successfully being able to attach to the gut wall.

Saracen Horse Feeds incorporate live yeast into the their performance and breeding rations, as well as some of our more specific special needs rations, such as Show Improver Mix and Cubes.

Approved Live Bacterial strains

Unfortunately, in the market there are reports of unapproved live bacterial preparations that are being marketed as probiotics (digestibility enhancers or gut flora stabilizers) being used within some horse feeds. 

The only micro-organisms currently permitted for horses in Europe are 4 strains of yeast (Saccharomyces cerevisiae).  They are:

Brand Name Additive Number
YeasSacc 4a1704
Levucell 4a1711
Actisaf 4b1702
Vistacell  4b1710

You can check yeast preparations to ensure that only authorized additives including probiotics are used in any products that you use by following the link to the EU register of approved feed additives for ease of reference - 

Final words: THINK HINDGUT, FIBRE AND FORAGE AND YEAST (AUTHORISED!)............ The rest will then seem easy!