What are FOS and MOS? Effects on Gut Health in Cats and Dogs

When choosing food for your cat or dog, check the ingredient list on the back of the package for FOS and MOS You may see the following expressions. At first glance, these seemingly technical terms describe two different components related to the gut environment. FOS is a prebiotic that can be used by some beneficial microorganisms in the gut. MOS, mostly derived from yeast cell walls, is considered among prebiotic components in many sources. The way they work in the gut is not the same. The structure of products containing MOS can also vary depending on the type of yeast used and the production method. The presence of FOS or MOS on the packaging can give a positive clue about the food. However, it is not correct to choose food based on a single component. The results obtained may vary depending on the amount used in the food, the overall formula of the food, and your pet's gut microbiota.

FOS is a prebiotic that can be used by some beneficial microorganisms in the gut. MOS, mostly derived from yeast cell walls, is considered a prebiotic component in many sources. The way the two work in the gut is not the same. The structure of products containing MOS can also vary depending on the type of yeast used and the production method.

The presence of FOS or MOS on the packaging can be a positive indicator of the food. However, choosing a food based on a single ingredient is not correct. The results obtained may vary depending on the amount used, the overall formula of the food, and your pet's gut microbiota.

FOS and MOS Sources and the Differences Between Them

FOS and MOS can be used together or separately in infant formulas aimed at gut health. Although they are mentioned for similar purposes, their sources and how they work in the gut are different.

FOS Nedir?

FOS is an abbreviation for fructooligosaccharide. It can occur naturally in plants such as chicory root and asparagus. FOS used in pet food is mostly obtained from chicory root or through enzymatic processes applied to sugars.

FOS can reach the large intestine of cats and dogs without being completely broken down by digestive enzymes. Here, it can be used as a nutrient source by some intestinal microorganisms. Because of this characteristic, it is classified as a prebiotic.

What is MOS?

MOS is an abbreviation for mannan oligosaccharide. MOS used in pet foods is usually obtained from yeast cell walls.

Yeast cell walls may contain other components besides mannan structures. Therefore, the phrase "yeast cell wall" on the label does not indicate that the product contains pure MOS or that the amount of MOS is specified. The product composition may vary depending on the type of yeast used and the production process.

The possible effects of MOS are being investigated through the processes by which some bacteria adhere to the intestinal surface and other interactions in the intestinal environment.

Property	FOS	MOS
Abbreviation	Fructooligosaccharide	Mannan oligosaccharide
Primary source	Cikori root, inulin-containing plant sources or enzymatic production	Yeast cell wall
Key role in the gut	By specific microorganisms Available	Interactions with some bacteria and intestinal components are investigated
Names that may appear on the label	FOS, fructooligosaccharide, oligofructose	MOS, mannan oligosaccharide, yeast cell wall

FOS and MOS can be found in the same food, but one is not a substitute for the other. Using them together does not automatically mean they will have a stronger effect.

How do FOS and MOS work in the gut microbiota of cats and dogs?

FOS and MOS act on the gut microbiota through different mechanisms. FOS is mostly associated with microbial fermentation. MOS, on the other hand, is studied in terms of the interactions it can establish with specific bacteria and different structures in the gut environment.

FOS and the Fermentation Process

FOS can reach the large intestine without being completely digested in the small intestine. Some microorganisms here break down FOS and use it as an energy source. This process is called fermentation.

Short-chain fatty acids can be formed during fermentation. These substances are not found in the structure of FOS itself. They are produced while gut microorganisms process FOS. So why are they important?

Short-chain fatty acids play a role in regulating the gut environment. For example, butyrate, a short-chain fatty acid, is one of the main energy sources of the cells on the surface of the large intestine. However, the amount formed and the possible results may vary depending on the type of FOS, the dose, other components of the food, and the animal's existing microbiota.

MOS and Bacterial Interaction

Some bacteria can utilize mannose-sensitive structures to adhere to the intestinal surface. It is suggested that MOS may bind to these structures, limiting the adherence of certain bacteria to the intestinal surface.

This mechanism may only apply to some bacteria that use mannose-sensitive attachment structures. The level of effect depends on the source of MOS, the production method, and the amount used.

What are the Possible Effects of FOS and MOS in Cats and Dogs?

The effects of foods containing FOS and MOS on intestinal microbiota and stool characteristics have been investigated in various studies.

FOS use may contribute to the following changes in some cats and dogs:

• Growth of certain gut microorganisms
• Changes in microbial fermentation products
• Support for certain stool characteristics
• Reduction of some stool compounds associated with bad odor

These results should not be expected in every animal. While some studies have shown changes in gut microorganisms, no significant difference has been found in stool consistency or compounds associated with bad odor.

MOS is being investigated for the following possible effects:

• Limiting the adhesion of some bacteria to the intestinal surface
• Changes in some groups in the gut microbiota
• Supporting the gut environment along with other components in the yeast cell wall

How to Identify FOS and MOS in Cat and Dog Foods?

When examining food labels, you may see the expression FOS as fructooligosaccharide or oligofructose. MOS, on the other hand, will appear as an abbreviation or its full name, mannan oligosaccharide.

Sometimes you may come across the phrase "yeast cell wall" directly in the ingredient list. This indicates that a yeast derivative containing mannan is used in the formula. However, it is important not to overlook a small detail here: The fact that "yeast cell wall" is written on the label does not mean that the product contains pure MOS or that the amount of MOS in it can be precisely measured.

The presence of the terms "chocolate root" or "yeast cell wall" on the label does not prove that the product contains a specific amount of pure FOS or MOS. These raw materials may consist of different components.

While ingredient lists help to understand the presence of the components used, the quantities are not always stated. The order in the ingredient list alone does not indicate the quality or clinical effect of the product.

The following points should be considered together when choosing pet food:

• Whether the product is a complete food or a supplementary product
• Suitability for the cat or dog's life stage
• Manufacturer's expertise in nutrition
• Quality control processes
• Nutritional research related to the product
• Usage instructions on the label
• The animal's current health status

What to Consider When Using FOS and MOS?

When switching to cat or dog foods containing FOS and/or MOS, a gradual transition can help reduce digestive problems in some animals. While the transition period varies depending on the animal's sensitivity, in most cases, gradually mixing the old and new food over 7 to 10 days is preferable.

The amount of digestive supplements, which may contain FOS and MOS, should not be exceeded as stated on the label. When more than one prebiotic or fiber product is used simultaneously, total consumption may increase unnoticed.

Giving excessive amounts or suddenly of fermentable ingredients can lead to problems such as gas, abdominal discomfort, soft stools, and changes in bowel frequency in some cats and dogs. Mild and short-term changes in stool consistency may occur during food transitions.

Important: Vomiting, weakness, loss of appetite, significant abdominal pain, bloody stools, black stools, recurrent diarrhea, or unexplained weight loss should not be attributed solely to a change in food. Fluid loss can develop more rapidly in puppies, elderly animals, or animals with chronic illnesses. In these cases, veterinary evaluation should not be delayed.

How to Choose Cat and Dog Foods Containing FOS and MOS?

For healthy cats and dogs, the priority is a food that is nutritionally complete, meets reliable production standards, and is appropriate for their life stage. The presence of FOS or MOS alone should not be the sole reason for selection.

When comparing food options, you can look for terms such as FOS, fructooligosaccharide, MOS, mannan oligosaccharide, or yeast cell wall by examining the product's ingredient list. When making this assessment, it is a more accurate approach to examine cat and dog foods separately according to age, life stage, and nutritional needs.

Frequently Asked Questions About FOS and MOS

What is the difference between prebiotics and probiotics in cats and dogs?

Prebiotics are components that are selectively used by certain microorganisms in the host organism and provide health benefits. FOS is one of the most researched prebiotics in this group.

Probiotics, on the other hand, are live microorganisms that are expected to provide benefits to the host organism when given in sufficient quantities. The effect of a probiotic depends on the microorganism strain it contains, the amount of live microorganisms, storage conditions, and duration of use.

Can FOS and MOS be used simultaneously with probiotics?

Prebiotic components can be found in the same product as probiotics. Products that combine live microorganisms with suitable components that these microorganisms can use, and are intended to provide health benefits together, are called synbiotics.

However, a product being defined as synbiotic does not, by itself, indicate that it is effective, necessary, or suitable for every animal. The product's content, intended use, storage conditions, and veterinary recommendations should be considered.

MOS prebiyotik midir?

MOS is frequently considered among prebiotic components in pet nutrition sources. However, its mode of action differs from classic fermented prebiotics like FOS.

Some effects of MOS are explained through the processes by which bacteria adhere to the intestinal surface. Therefore, classification may vary depending on the scientific definition used and the evidence available about the product.

How long does it take for FOS and MOS to show effect?

There is no fixed duration of effect for FOS and MOS that applies to all cats and dogs. The response may vary depending on the product used, the amount, the diet, and the animal's existing intestinal microbiota.

It is not correct to expect a definitive result after a few days of use. Stool consistency, bowel regularity, gas, appetite, and general health status should be monitored together in evaluating the product.

Can FOS or MOS be given to kittens and puppies?

FOS or MOS may be included in the formula of complete foods specifically for young animals. This should not be interpreted as meaning that a separate supplement can be used indiscriminately.

Additional products should not be given without evaluating the age, weight, current food, and health status of the puppy. Puppies with diarrhea, vomiting, or growth retardation should be evaluated by a veterinarian.

Can FOS or MOS be given to a cat or dog with diarrhea?

FOS and MOS do not determine the cause of diarrhea and do not provide treatment alone. If diarrhea persists or is accompanied by vomiting, weakness, loss of appetite, bloody stools, or abdominal pain, a veterinarian should be consulted.

Is food containing FOS and MOS of higher quality?

The presence of FOS or MOS does not, by itself, indicate that a food is of higher quality. Nutritional adequacy, life stage, production standards, and the overall formula should be evaluated together.

Can FOS and MOS be used daily?

FOS and MOS can be included in daily feeding as part of a complete food formula in appropriate amounts. Long-term use of separate supplement products should be evaluated according to the product's content and the animal's needs.

References

Wilson SM, Swanson KS. The influence of ‘biotics’ on the gut microbiome of dogs and cats. Veterinary Record. 2024;195:2–12. doi:10.1002/vetr.4914.

Pilla R, Suchodolski JS. The gut microbiome of dogs and cats, and the influence of diet. Veterinary Clinics of North America: Small Animal Practice. 2021;51(3):605–621. doi:10.1016/j.cvsm.2021.01.002.

World Small Animal Veterinary Association. Selecting a Pet Food for Your Pet. Global Nutrition Toolkit.

World Small Animal Veterinary Association. Nutritional Assessment Guidelines.