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MOS: you probably come across it often on pet food labels. But what exactly is it, and how does this ingredient work in the diet?

MOS stands for mannan oligosaccharides: short chains of mannose, a sugar molecule structurally similar to glucose. Because of the particular way these mannose molecules are linked, MOS is not readily broken down by the dog’s and cat’s own enzymes. In pet food they usually come from yeast cell walls.

🦠 An alternative place to attach
Some bacteria have structures with which they can attach to the gut wall. Certain of these bacteria also recognise the mannose structures in yeast cell wall products. The mannose structures in MOS can thus offer such bacteria another place to attach to. Hence the nickname: the decoy.

🔬 From mechanism to effect
The ability of bacteria to bind to a yeast product has mainly been studied in the laboratory. Binding varies between bacteria and between products. But what happens when MOS is fed to a dog or cat? Studies show that diets with MOS or yeast cell walls can influence the composition of the gut microbiota and some immune parameters. However, the products studied often also contain other substances, such as beta-glucans. This makes it difficult to establish which part of the effect is due specifically to MOS. In addition, changes in an immune parameter do not necessarily mean that the animal is “healthier”, or that in the case of a gut disorder the signs will then decrease. It only tells us that “something” is happening. Whether that “something” is good or bad is very hard to determine.

🩺 What use is it in practice?
MOS is therefore added to some diets to support gut health. But we do not yet know enough about how much MOS is needed for this in dogs and cats. Scientific studies use different amounts and often whole yeast cell walls, which also contain other substances. They are therefore hard to compare and not easy to translate into what we can expect in practice.

The statement “with MOS” on a package is therefore not, in itself, a reason to choose a diet. But that of course does not mean that MOS is insignificant or has no place in a fibre-based approach to gut problems. It only means that today we do not yet know exactly what to expect from it.

Next edition: beta-glucans, the diverse family. They occur in yeast and cereals, among other sources. But apart from their name, do they also share the same properties?

🥣 Meet the Fiber: a FeedWise series on dietary fibre in dogs and cats. Each edition covers one fibre: its mechanism of action, indications, limitations and place in clinical practice.

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