This is a hot topic for the equestrian industry, as horses' suffering with ulcers and gut imbalances is becoming more apparent to owners. So, what really is best - prebiotics, probiotics or both?

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The team of vets at Synovium are asked this question frequently, so decided to perform extensive trials and scientific research to form their professional verdict on this topic.

Dr SHL Donker DVM, FEI Dutch veterinarian & Synovium Horse Health founder, and Synovium UK managing director Vicky Hipkins cover the topic in our latest guest post.

Whilst some research has been completed using probiotics on horses (largely in foals) it is neither extensive, nor conclusive. Supplementing with probiotics is mainly based on research of probiotics for humans.

As horses are mainly grass eaters and not meat eaters like humans, we cannot compare the two!

What are probiotics?

Probiotics are live microorganisms contained in a feed or supplement product.

It is believed that, when fed to horses, there is an increase of the beneficial bacteria needed for digestion to counteract digestive upset caused by an imbalance in bad and good bacteria in the hind gut. However, there is no conclusive evidence in horses that this works, and some studies have shown that some probiotics can cause further upset. This is because each individual horse has unique microbiotics, which are determined at just a few days old. There are just too many factors which affect the numbers and types of good bacteria in any individual horse - from feed to biological chemistry - to fully understand if probiotics make any difference.

Understanding how the horse’s gut works

Horses are hind gut fermenters - meaning that the large intestine is where fermentation of ingested fibre takes place. The fibre is the main component of the horse’s forage such as grass and hay, it is broken down by microorganisms to produce essential nutrients that are absorbed through the horse’s colon.

Understanding the horse's gut diagram

Because the bacterial and protozoal flora of the hindgut are geared for fibre fermentation, it is susceptible to receive large amounts of undigested sugars in the large intestine causing gut upset.

The correct balance between these good microbes in the equine hind gut and harmful bacteria can be easily upset when:

  • starch that does not get digested from concentrated feeds ends up in the hind gut
  • horses spend hours without forage to consistently graze on
  • a sudden change in forage or feed without slow introduction (7-10 days at least is recommended)
  • stress and anxiety occurs

It's important to keep the balance of good and bad bacteria exactly right for each individual horse.

Supplementing with prebiotics

Prebiotics are a non-digestible food source for your horse's existing good gut microbes. They do not contain live bacteria or other microorganisms, as with probiotics. Prebiotics support the horse's existing balance of bacteria in their gut by stimulating growth and activity of the existing microorganisms, so the helpful bacteria remain healthy and active to prevent the bad bacteria thriving. Studies have proven the benefits of supplementing horses with prebiotics.

Synovium® Gastrosafe

Synovium's team of leading vets has studied scientific evidence for horse gut support and undertaken extensive trials to provide a supplement that effectively supports the horse’s front and hind gut.

Gastrosafe has a unique veterinary formula supporting a healthy stomach environment and aiding digestive function. It helps to control gastric acidity in horses, providing essential prebiotics, whilst supporting the natural anti-inflammatory processes in the front and hind gut. It has been scientifically proven to support horses during or after veterinary treatment for ulcers when fed for at least six weeks. Always speak to your vet first if you suspect your horse has ulcers.


Synovium Gastrosafe contains (daily dose is based on maintenance for an average 500kg horse)

  • Calcium Carbonate, 10,000 mg per daily dose - a natural buffer against stomach acid
  • Laminaria hyperborean, 5,000 mg per daily dose - seaweed, very palatable vitamins, minerals and trace elements to help protect the stomach wall
  • Magnesium Hydroxide, 5,000 mg per daily dose - helps to neutralise stomach acid and is often used to calm horses who easily get stressed or anxious.
  • Fructooligosaccharides, 5,000 mg per daily dose - prebiotics, a natural feed source for good gut microbes
  • Glutamine Peptides, 1,900 mg per daily dose - an essential amino acid to help maintain a healthy stomach lining and replenish the natural L-glutamine which is often lost through stress
  • Threonine, 2,360 mg per daily dose - an important amino acid for optimal GI tract health by assisting mucin production to support a smooth gut function and nutrient absorption. Also guarding the gut from bad bacteria and toxins.

Full details can be found on the Synovium website

Knowing what is best to feed your horse to support gut health is still an ongoing study and therefore it is always recommended to speak to your vet for advice. There are many theories on probiotics but nothing concrete, unlike with prebiotics. Synovium Horse Health bases its supplements on only proven science and trials.