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No Guts, No Glory! Microbes Are Key to Gut Health

From TV ads to newspaper articles to health-and-wellness — even dog enthusiast — websites, you’ve undoubtedly come across the terms microbiome and microbiota. What are these things, and why should you care? We’ll explain not only what the gut (or more properly, gastrointestinal [GI]) microbiota is, but what it means for your dog with a sensitive stomach.

What is the gut microbiota? How is it different from the gut microbiome?

The gut microbiota, which used to be called the gut microflora, is the population of bacteria, viruses, fungi (e.g., yeast) and other single-celled microorganisms that live in the GI tract. The gut microbiome, on the other hand, refers to all of the genes belonging to those gut microbes. The two terms are sometimes used interchangeably, although the differences seem subtle.

Your dog’s GI tract is home to trillions of microorganisms, the vast majority of which are bacteria. In fact, scientists estimate that gut microbes outnumber a host animal’s body cells by a factor of 100. That puts the total number of microorganisms in the range of 1010 to 1014 (that’s 1 with 10 to 14 zeros after it!).

Your dog’s gut microbiota is as unique as he or she is. But although every dog has a unique microbial community, its physiological functions are always the same. More on those in a moment.

Where does the gut microbiota live?

Sure, the answer seems obvious — the gut microbiota can be found in the gut. But what part of the digestive system comes to mind when you read or hear the word gut? Do you think of the stomach? Or colon? What about the mouth?

The GI microbiota is one of the densest microbial populations on the planet and very different communities of bacteria can be found in the stomach, small intestine and colon. (The oral microbiota is considered a separate population.) The number of bacteria and the diversity of species increase gradually along the digestive system, starting with the stomach. The diversity and numbers of bacteria are greatest in the large intestine. Some bacteria are found living on the surface of the stomach or intestinal lining, within glands (e.g., gastric glands of the stomach) or in the mucus coating that lines the intestines. Still other bacteria are present in the material passing through the GI tract.

Why is the gut microbiota important?

GI microorganisms play important roles in several vital functions — digestion is just one of them. The microbiota:

  • Stimulates the immune system
  • Helps defend against disease-causing microorganisms
  • Helps with digestion of certain food components
  • Produces some vitamins, such as biotin, folic acid and vitamin K
  • Helps the lining of the intestine to develop properly

Considering all the roles the gut microbiota plays in normal body function, it’s no surprise that many experts now consider it an “acquired organ.” Puppies are born with sterile GI tracts but begin developing their own microbiota when they’re exposed to their mother’s microbiota during birth, nursing and cleaning. A newborn puppy’s entire GI tract is usually colonized within 24 hours. The microbial community then evolves over several months into a more typical adult population. This early microbiota is critical for “teaching” the gut-associated immune system to tolerate normal bacterial and food antigens (substances that cause the immune system to respond).

The GI microbiota also helps defend your dog’s body against undesirable and disease-causing organisms in several cool ways:

  • Competing for nutrients and attachment sites
  • Producing antimicrobial compounds
  • Altering gut pH
  • Assisting with the time it takes for food to move through the GI tract
  • Producing vitamins and growth factors for intestinal cells

When it comes to nutrition, the microbiota helps break down some components of food, such as dietary fibers, that would otherwise not be used. Bacteria in the large intestine ferment some dietary fibers, such as tomato pomace and dried chicory root, to produce short-chain fatty acids (SCFAs) that can be used by intestinal cells for energy. SCFAs also can modify intestinal movements and the passage of food through the digestive system.

What’s the link between a dog’s sensitive stomach and gut microbiota?

Changes in the composition and/or diversity of the GI microbiota is known as dysbiosis. In some dogs, changes in bacterial population numbers accompanied by a decrease in microbiota function may cause diarrhea and other GI-related signs. In other dogs, an underlying intestinal disease may cause dysbiosis. According to Jan Suchodolski, a board-certified veterinary microbiologist and associate director of the GI Laboratory at Texas A&M University, dysbiosis occurs in most dogs with GI disease, either along the full GI tract or limited to the small or large intestine.

Dogs with sensitive stomachs tend to have sporadic but recurrent loose stools, occasional vomiting and too much nasty-smelling gas. Although there are no studies that document dysbiosis in dogs with sensitive stomachs (which isn’t a true diagnosis), research does show changes in the microbiota of dogs with either acute (sudden onset) or chronic diarrhea.

Can dog food choices affect the gut microbiota?

Certain components of the diet — such as fiber, protein and fat — can affect particular members of the gut microbiota. However, more research is needed before this question can be completely answered. Far more is known about the human gut microbiota and microbiome than about the canine microbiota and microbiome.

One area of interest to researchers is the role of the gut microbiota in canine obesity. In a recent study, scientists explored the influence of protein-to-carbohydrate ratio on the gut microbiome in dogs with different body conditions (i.e., overweight versus lean). The study found that protein and carbohydrate content of the diet can change the composition of the gut microbial community, and the effect was more apparent in overweight dogs than in lean dogs. Researchers believe the information will help them use prebiotics, probiotics and other dietary interventions to influence the gut microbiota and provide an alternative therapy for obesity in dogs.

What’s the bottom line?

Advances in technologies such as gene sequencing are helping animal nutritionists and scientists to learn much more about the true microbial community of the GI tract. And while they’re learning more about the role of the gut microbiota in both health and disease, they realize there’s tremendously more to learn. But one thing is becoming clear: the GI microbiota is important to nearly every aspect of pet health.

 

RELATED POST: Digestion: From One End of Your Dog to the Other

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