If you’ve not read the previous post on supplements, here’s a quick reminder of the 5 categories of gastric supplement ingredients and how they work:

Probiotics – these are the ‘good’ bacteria in the gut, yeast such as saccharomyces cerevisiae.

Prebiotics – these are the foods of the ‘good’ bacteria in the gut, FOS and MOS for instance.

Substances that are slimy – these protect the lining of the stomach and gut, protecting it from being scratched by food passing through and some stomach acid. Linseed oil, pectin and beta glucans are good examples.

Substances that have a neutralising effect on the stomach acid – calcium and magnesium, for example.

Substances that remove/destroy or help the body to protect itself from harmful toxins and ‘bad bacteria’.



Apple pectin – a slimy one! Pectin acts as a barrier for the gastric mucosal membranes against excess gastric acid. (Source: https://forageplus.co.uk/the-egusin-concept-ulcer-prone-horses/)

Beta glucan – a prebiotic and a slimy one. It “is extracted from the inner cell wall of the yeast Saccharomyces cerevisiae. It is a highly efficient mycotoxin adsorbent. As such, it works to minimize, decontaminate and thus control the toxicity produced by fungi and molds ingested with unavoidably contaminated forage and feeds.” (Source: http://www.succeed-equine.com/education/yeast-for-horses/) “Beta-glucan gels in the stomach act as a coating for the stomach lining.” (Source: https://forageplus.co.uk/the-egusin-concept-ulcer-prone-horses/)

Calcium carbonate – an antacid

Dicalcium phosphate – an antacid

Fructo-oligosaccharide (FOS) – one of the most common pre-biotics. “Fructo-oligosaccharides (FOS) are found and derived from various different sources including artichokes, chicory, onions and sugar beet”.(Source: https://www.baileyshorsefeeds.co.uk/downloads/24430) FOS is a source of energy for the the beneficial microbes in the horse’s gut.

Lecithin – “also contains natural antioxidants which aid in protecting the muscle cells from degradation by free radicals.” (Source: https://forageplus.co.uk/the-egusin-concept-ulcer-prone-horses/)

Magnesium hydroxide/Carbonate/Oxide –  an antacid. “The ability of any compound to neutralise acid is determined by a combinations of pKa (the higher the pKa the more alkaline a compound is and the more acid it can neutralise) and the amount fed: Magnesium oxide (pKa = 15.7); Magnesium hydroxide (pKa = 15.7), Magnesium carbonate (pKa = 6.1). So the best magnesium compounds for neutralising stomach acid (hydrochloric acid) are Magnesium oxide and Magnesium hydroxide.” (Source: Dr David Marlin on Facebook)

Mannan oligosaccharide (MOS) –  one of the most common pre-biotics. It “is extracted from the outer cell wall of Saccharomyces cerevisiae. Its primary role is the competitive blocking of bacterial lectins. Bacterial lectins have an affinity to bind with glycoproteins that are attached to the membrane of intestinal enterocytes (cells responsible for nutrient absorption). This is the first stage of infection. Mannan mimics these intestinal glycoproteins, providing an alternative attachment site that competitively binds with pathogenic bacteria, rendering them unable to attach to the gut lining. Thus prevented from binding to the enterocytes, the bacteria are flushed from the system.” (Source: http://www.succeed-equine.com/education/yeast-for-horses/) (Bio-MOS is the same thing, it’s just a trade name).

Nucleotides –  a prebiotic that “enhances the maturity and growth of normal enterocytes, the cells lining the gut and responsible for nutrient uptake and pathogen defense. Although the body can synthesize nucleotides de novo, the process uses more energy than scavenging them from dietary sources. In addition to ongoing maintenance, cell division is critical for repairing damaged tissue, including ulcers. In times of stress or injury, dietary nucleotides may be indicated.”(Source: http://www.succeed-equine.com/education/yeast-for-horses/)

Seaweed buffer – mainly an antacid. Seaweeds often contain a high calcium content and therefore act as an antacid.  The supplement Equine 74 says the seaweed it uses  (Lithothamnium Calcareum) has a unique sponge-like structure helps absorb the acid. (NB I had some of this from the vet and Abbey ate round or spat out the tiny pellets!)

Sodium bicarbonate – an antacid

Yeast/Yea Sacc/Brewers Yeast – these are all the same thing; a strain of yeast called Saccharomyce Cerevisie!

As the name suggests, Brewers Yeast is yeast that is a by-product of the brewing industry.  It is dead and is a prebiotic.

Yea-Sacc is alive and a probiotic.

Supplementing a horse’s diet with  Saccharomyce Cerevisie is supposed to help the hind gut, although there’s lots of different theories as to how it works. Some say as a pre-biotic, it’s the thioredoxin yeast contain that acts as an antioxidant and anti-inflammatory. As a pro-biotic it is said to be beneficial for the growth of good bacteria in the hind gut.

There are other strains of yeast which are occasionally found in supplements, but in preparing my spreadsheets of supplements in the UK, I’ve only seen one (Yarrowia lipolytica which is in Equinox Gastro-U and a prebiotic)!

Trademarked products found in supplements: 

Protexin – as in ‘Protexin probiotics’ . Protexin is a company: “Protexin Healthcare is dedicated to producing innovative, research based live bacteria products of the highest quality…”

Preplex® prebiotic -Fructo-oligosaccharide made by the company Protexin.


Because feed is such a complicated issue, I’ve written a number of blog posts sharing my research and my decision making process: