Prebiotics and probiotics quiz

What do prebiotics and probiotics really do?

By Ann Wortinger, BIS, LVT, VTS (ECC, SAIM, Nutrition)

It seems that everywhere we look these days we are seeing products that include either probiotics or prebiotics.  This can be in the form of supplements, known as nutraceuticals, or in over-the-counter foods and therapeutic diets. 

According to the currently adopted definitions by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), probiotics are: “living microorganisms which when administered in adequate amounts confer a health benefit on the host”, whereas prebiotics are “non-digestible food ingredients that selectively stimulate the growth and activities of specific bacteria in the gastrointestinal tract and exert beneficial effects on the host”.  The Food and Drug Administration (FDA) defines nutraceuticals as “nondrug substances produced in a purified or extracted form and administered orally to provide agents required for normal body structure and function with the intent of improving health and wellbeing”.

As seen by these definitions, we are either talking about bacteria or substances that benefit bacteria in the intestinal tract.  We know that there are millions of bacteria that normally reside in the small and large intestines of normal, healthy animals.  These bacteria help with digestion of food, maintain intestinal mucosal integrity, and participate in metabolism, as well as local and systemic immune stimulation.

The intestines

The intestines are seen as the largest immune system in the body, compromising approximately 70% of the total system.  The mucosal barrier found in the intestines helps to block the entrance of most pathogenic bacteria into the body while allowing the entrance of permeable nutrients.  Since most pathogens enter the body through the mouth and then the intestinal tract, these intestinal defences must be working optimally to cope with the onslaught of foreign substances and pathogens to which it is constantly exposed.

This defence involves the coordination of three different systems within the intestines; the first are the resident intestinal microflora, which provide an environment that favour the growth and functioning of beneficial bacteria. The second is the intestinal mucosa, which provides a protective barrier against pathogenic bacteria; and lastly, the gut-associated lymphoid tissue (GALT). There is substantial research being done looking at how enteral nutrition can be used to help improve the GALT and intestinal mucosa barrier.  Hopefully, we will see the benefits of that research in the next few years.  Currently, we are using prebiotics and probiotics to help with this modulation.


Typically, prebiotics are a type of carbohydrates called oligosaccharides, though by definition non-carbohydrates can also be classified as prebiotics.  The ones used most frequently are classified as soluble fibres.  These were first identified as a functional food with only two classes of fructooligosaccharides fully meeting the definition of a prebiotics.  These would include oligofructose and inulin.

Oligofructose is a 2-8 chain fructose-based saccharide molecule that undergoes fermentation fairly quickly in the colon providing nourishment to the bacteria in that area.  Examples of sources for fructooligosaccharides (FOS) include soybeans, oats, beets, and tomatoes.

Inulin is a longer 9-64 chain fructose based saccharide that tends to be fermented more slowly, benefiting bacteria farther down the colon.  It can also be broken down into the FOS by intestinal bacteria to provide both FOS and inulin.  Inulin can be found in Jerusalem artichoke, jicama, and chicory root.

These two fibres are seen as minimally digestible because of their beta bond connecting the fructose molecules.  Dogs and cats lack the enzyme in their intestines to break down the beta bond; instead they usually break down alpha saccharide bonds.  The resident bacteria in these animals have the ability to break the beta bond producing short chain fatty acids (SCFA).  The SCFA seen most commonly include acetate, propionate, and butyrate.
The SCFA produced by the breaking of the beta bond through bacterial fermentation serve as an energy source for the colonocytes, act to lower the colonic pH, and stimulate sodium and water absorption.  One SCFA in particular, butyrate, serves as a primary source of energy for colonocytes, but may also directly enhance cell proliferation of normal cells, while suppressing proliferation of transformed cells.  Studies have shown there are generally positive effects on gut microflora, host health as evaluated through gut integrity and bacterial colonization, and animal performance as evaluated through digestion, body weight gain, and feed efficiency when FOS and fructose based inulins are added to the diet.


Probiotics, rather than encouraging the growth of beneficial bacteria and suppressing the growth of pathogenic bacteria, actually introduce these beneficial bacteria into the environment.  To be able to function as probiotics, the bacteria being used must meet certain criteria.  They must be able to:

  • Survive the acid and bile found in the gastrointestinal tract
  • Adhere to the intestinal cells
  • Exclude or reduce pathogenic bacterial adherence
  • Produce acids, hydrogen peroxide and/or bacteriocins that antagonize the growth of pathogens
  • Co-aggregate to help achieve normal balanced microflora population
  • Be safe, noninvasive, noncarcinogenic, and nonpathogenic to the animal

Initially, the gastrointestinal tract of a newborn is sterile, but is colonized with bacteria within hours of birth.  These bacteria find their individual niches within the intestinal tract and reach a state of equilibrium. 

The primary bacterial populations included in probiotics that are seen to benefit the cat and dog are lactic acid bacteria, especially Lactobacilli, Bifidobacteria, and Enterococci.  These bacteria use fermentation to transform some sugars into organic acids, particularly lactic and acetic acids.

Probiotics can benefit the intestinal microflora in a number of ways.  They can increase the fecal bacteria count of good bacteria while decreasing the numbers of pathogenic bacteria.  Some probiotics have been shown to minimize adherence to the intestinal epithelial cells and establish pathogenic bacterial populations.

Probiotics can also help to control diarrhea caused by bacterial overgrowth or parasitic infection.  This uses the principles of competitive exclusion, the competition for nutrients and binding sites and an increase in specific and nonspecific immune response.


Since prebiotics are used as both a source of nutrition for the colonocytes and as a fibre source for the animal, inclusion in the diet is fairly easy.  Unlike prebiotics, the use of probiotics is more of a transient process based on need rather than a long-term process.  Ideally, the body will supply the bacterial population to support the best intestinal health.  But when this doesn’t occur, or when challenges are expected that could affect intestinal health, probiotics can be easily added into the diet to help support the bacterial populations there. 

When evaluating products to use for either prebiotics or probiotics, ensure that there is research to support the claims given, that the product is proven to contain the stated levels of additives, and that they have been proven to promote normal intestinal microflora.  A review of probiotics in commercial dog and cat foods by Dr. Scott Weese demonstrated that few products meet these guidelines.  Alternately, evaluation in a controlled clinical setting can provide firsthand knowledge of the effectiveness of the products used.  By looking at these facts, you can ensure that you are providing the best product to support a happy, healthy intestinal tract with a hard-working population of beneficial bacteria.


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Pan X, Chen F, Wu T, Tang H, Zhao Z.  Prebiotic oligosaccharides change the concentrations of short-chain fatty acids and the microbial population of mouse bowel. Journal of Zhejiang University Science B 2009; 10(4); 258-263.

Roberfroid M.  Prebiotics: The concept revisited.  Journal of Nutrition 2007;137:830s.
Verdonk JMAJ, Shim SB, van Leeuwen P, Verstegan MWA.  Application of inulin-type fructans in animal feed and pet food. British Journal of Nutrition 2005;93 supplement 1:s125-s138.

Weese, JS, Arroyo L.  Bacteriological evaluation of dog and cat diets that claim to contain probiotics.  Canadian Veterinary Journal 2003; 44:212-215.

This article is based on Ms. Wortinger’s presentation at the American College of Veterinary Internal Medicine Forum in National Harbor, MD.CVT