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Intestinal Microbiota. Role of Pre- and Probiotics in Dog and Cat Food

Role of intestinal microbiota

We are whole worlds, each and every one of us, as are our furry friends.  We go about our day without a thought for the healthy load of microorganisms that we carry.  They have populated our planet for over 3.5 billion years and played critical roles in the evolution and functioning of all living organisms. Species associated with the human and animal body are represented mostly by bacteria, and they colonize skin, mucosal surfaces and the gastrointestinal tract in large numbers. In the intestine the number of microorganisms (intestinal microbiota) can reach approximately 1014 which is 10 times higher than the number of cells in the human body.  The number of genes in these micro-organisms (collective “microbiome”) is approximately 3.3 million, which is at least 100 times higher than that in the human body.

Most researches today have focused on intestinal microbiota in humans since it is involved in gastrointestinal disorders including inflammatory bowel disease, cancer, irritable bowel syndrome and many metabolic diseases such as obesity, diabetes and metabolic syndrome. Microbiota may be implicated in neurologic conditions, and products of bacterial metabolism may affect not only the gastrointestinal tract but also our behavior, indicating communication between the digestive system and the central nervous system (gut-brain axis). To study microbiota, the National Institute of Health launched the Human Microbiome Project in 2007 with the goal of analyzing microbiota that normally inhabits the human digestive tract, skin, mouth, nose, and vagina.

The body’s microorganisms perform various functions essential for our survival. Although some microorganisms are pathogens, most of them are harmless or even beneficial. Some microbes produce vitamins and other essential nutrients. Yet others metabolize food that cannot be digested by the host. They also break down drugs and toxins, and regu­late many aspects of the immunity, protecting the body from infections and chronic inflammation, as well as many immune system disorders.

The highest number of microorganisms is in the gastrointestinal tract, particularly in the colon where they make up most of the flora and 60% of the dry mass of feces.  Colonization of the gut begins at birth with the first exposure of the newborn to the flora of the birth canal.

Dogs and cats have live with us for thousands of years; according to recent estimates, our association with dogs goes back 30,000 years. The health and well being of these companions, and well as our own health, depend very greatly on gut microbes. Despite this, there is still not much information on the microbiota of our companion animals.

One of the leading reasons for veterinarian visits is gastrointestinal disorders. Maintaining a healthy digestive system includes keeping a balance among the billions of bacteria colonizing the guts of our companions, since disturbances in the intestinal flora can lead to health problems such as indigestion, lowered immunity and susceptibility to diarrhea. The balance is a delicate one and is easily upset by antibiotics, poor diet or stress, which results in a condition called dysbiosis, and that in turn can express as various kinds of illnesses.


For maintaining a healthy microflora the use of probiotics has been recommended for some time now, and recently prebiotics have been added to the list.  Probiotics or "good bacteria" are live microorganisms that are the same as or similar to microorganisms living in the body, while prebiotics are substance that promote their growth or function.

While specific strains of probiotic or their combinations have been used in human nutrition as food supplements since 1980th, it was the Nobel laureate Ilya Metchnikoff who suggested the possibility of colonizing the gut with beneficial flora as far back as the early 20th century. A variety of probiotics are in use for reduction of gastrointestinal discomfort or strengthening of the immune system in humans. Probiotic products aimed at pets, especially dogs and cats, have also gained popularity among their owners as science provided the first products with proven efficacy.  The most beneficial of them belong to Bifidobacterium and Lactobacillus genera.

There are several reasons why probiotics are beneficial to health. These include competition for nutrients and adhesion sites with potential pathogens, production of antibacterial compounds, effect on microbial metabolism and immunity. Other possible benefits of probiotics in pets are associated with help in stress management, protection from infections caused by enteropathogens, increased growth and development, control of allergic disorders and obesity.

In the early days proboitics used in companion animals’ nutritional therapy were not originally derived from the canine or feline intestinal microbiota. However, their intestine is rich in microorganisms with probiotic potential and microorganisms that come from the same species might be the most appropriate probiotics source.

Dogs and cats have distinct bacterial species that differ and also vary in different dog and cat species living in different geographical areas. Domestic animals have high numbers of microorganisms in the gastrointestinal tract that outnumber those living in the human gut. Microbial diversity and concentration increase along the length of the gastrointestinal tract reaching the highest numbers in the colon. Also the composition of microbiota and its metabolism in the animals gut depends on the feed, its content and nutritional value.

Several studies show that probiotics have been successful in the prevention and treatment of acute gastroenteritis, inflammatory bowel disease and prevention of allergy in companion animals. Probiotics are beneficial after antibiotic therapy that is used commonly to treat certain diseases. Antibiotics often reduce the population of beneficial bacteria, increase the levels of potentially harmful microorganisms and also lead to antimicrobial resistance. In addition, antibiotic therapy might have a long-term effect on intestinal microbiota even after its suspension. It is known also that microorganisms with antimicrobial multiresistancy, such as ampicillin- and tetracycline-resistant enterococci, may transfer from pets to pet and even to their owners.


Prebiotics are substances that stimulate the growth or activity of beneficial microorganisms presumably bifidobacteria and lactic acid bacteria. These beneficial effects include, improving digestion and stimulating the immune system.

Natural prebiotics are mostly non-digestible fibers that pass through the gastrointestinal tract into colon and stimulate the growth or activity of colonic  microbiota. Many plants (chicory root, Jerusalem artichoke, dandelion, garlick, leek, onion, asparagus, wheat bran and others) are rich in prebiotic fibers. Research shows that use of prebiotics in human improve absorption of minerals,  immune system effectiveness and bowel acidity, increase frequency of defecation while reducing colorectal cancer risk, inflammatory bowel disease and hypertension. The mechanism of these effects is not clear but research demonstrates that they increase food fermentation and production of short chain fatty acids (propionic, butyric, acetic). The short-chain fatty acids, particularly butyric acid, is important for colon health because it is the primary energy source for colonic cells. It also has anti-carcinogenic as well as anti-inflammatory properties. Butyric acid inhibits the growth of tumor cell and induces apoptosis or programmed cell death of human colorectal cancer cells.

Several studies on the use of prebiotics in canine feeds suggest that dogs may benefit from their addition to the diet. Healthy dogs fed a diet supplemented with chicory demonstrate firmer fecal consistency, lower fecal pH, increased levels of bifidobacteria and decreased counts of pathogenic bacteria from Clostridium in their stools.


New types of prebiotics are being constantly developed and they seem to be a promising additive to animal feed. The consumption of fermentable prebiotic polydextrose (synthetic polymer of glucose) by dogs was reported to increase fecal short chain fatty acids levels, while decreasing fecal pH and some harmful metabolites concentration.

The effects of dietary fibers supplementation on the  microbiota in cats have also been described. Additions of prebiotics to feline diet positively affect gut microbial populations. Cats fed diet supplemented with fructooligosaccharides (carbohydrate made of fructose molecules) or beef pulp had increased bifidobacterial level in feces, while the count of E. coli was decreased. More research is needed to reveal the potential benefits of other fibers sources that can be used in canine and feline diets for healthy and diseased animals.

In conclusion, the intestinal microbiota plays an important role in the well-being of humans and their companion animals. Current studies suggest that specific probiotic strains or their combinations, as well as prebiotics, may be useful in the canine and feline nutrition, therapy and care. The most appropriate approach is to use probiotics prepared from the host-derived microorganisms.

Rafail Kushak, Ph.D, Dr. Sc.
Massachusetts General Hospital, Harvard Medical School

VetVittles sincerely appreciated the article of renown scientist Dr. R. Kushak. The ideas of this article inspired the creation of Microbiome Seed by VetVittles


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