As a quick refresher from our first medium article, the microbiome refers to the ecosystem of bacteria and other microorganisms living on or inside an animal. These commensal bacteria are those that neither cause harm nor benefit to their host, in this case, canine. Here we are talking about the gut microbiome, the gastrointestinal tract, specifically. Each dog has a gut microbiome that is unique.
There are several factors that influence microbiome: age, breed, weight, exercise levels, genetics, antibiotics taken, and more. In this article we will examine diet, as perhaps the top environmental contributor to gut microbiome composition and diversity.
Which bacteria comprise canines’ microbiome?
The majority of canine microbiome can be found in the intestines. The small intestine is home to both anaerobic and facultative anaerobic bacteria, while the large intestine only is home to anaerobes.1 Anaerobic bacteria are those that can only grow and survive without any oxygen present. Facultative anaerobic bacteria can grow and survive with or without oxygen present. This limits what bacteria will survive in animal’s digestive tract, since some do require oxygen to survive.
When categorizing bacteria, we use taxonomic designations, that classify various types of organisms based on their features and key characteristics. For microbiome studies, we typically evaluate bacteria at the Phylum and the Genus level.
There are three main bacteria phyla that tend to dominate the canine microbiome: Bacteroidetes, Firmicutes, and Fusobacterium [1]
**Please refer to Table 1 for a listing of all Phyla, and key genera within each.
Table 1: The most common phyla and respective genera present in the dog gut microbiome.
Adapted from: Bartges, J. Gut Microbiome and Obesity. Hill’s Global Symposium, 2019.
Typically, each bacteria or group of bacteria play a specific role to break down macronutrients in the intestines: fats, proteins, and carbohydrates. For example, when a dog is fed a specific diet with a specific macronutrient composition, this will have an impact on the bacteria present in the gut. This happens because the bacteria rely on a specific macronutrient as its energy source, or its metabolic activity [2]. Essentially, the macronutrients are “food” for the bacteria, and each bacterium prefers a specific cuisine.
To make the discussion more straightforward, let’s take two specific dry food diets: high protein-low carbohydrate (HPLC) and high carbohydrate-low protein (HCLP). A pivotal study by Li et al.4 established that in a HPLC diet, there was in an increase in Clostridiaceae, Lachnospiraceae, and Ruminococcaceae bacterial genuses and a decrease in Erysipelotrichaceae, Veillonellaceae , and Lactobacillaceae bacterial genuses. This study also showed that there was a higher ratio of Bacteroides: Prevotella species in the HPLC diet. On the reverse side with a HCLP diet, there as an increase in Bacteroides and Firmicutes as well as a 4.6x increase in Prevotella vs. the HPLC diet. There was also a higher ratio of Bacteroides: Firmicutes phyla in the HCLP diet.
What is Prevotella?
Given the immense increase in prevotella among HCLP diets, let’s dive deeper into this particular bug. Prevotella is a genus classification within the Bacteroidetes phylum, with many species. It is an anerobic, single-cell, non-motile bacteria that lives in our dog’s gut. Prevotella has shown to have a strong association to the levels of carbohydrates, especially those derived from plants.4 This is because the purpose of Prevotella is to help breakdown complex carbohydrates, present in fruits and veggies. This species can breakdown tough fibers like xylan in plants (like the grass our pups are bound to eat) but also simple sugars like glucose. Prevotella is also associated with different types of gastrointestinal diseases, usually a decreased abundance of Prevotella along with other species. This decrease of bacterial species reduces the energy source (short chain fatty acids) for the cells in the colon.
Scientists at DIG labs are learning how to use Prevotella as a biomarker for carbohydrate load in a dog’s diet. This is important because, despite pet parents’ best attempts to balance a diet, carbs can sneak in, through treats, table scraps and more, and create a macronutrient imbalance, especially when there is a weight management or chronic condition being managed.
Why are the dietary microbiome differences important?
In the HCLP diet, overrepresentation of carbohydrate digestion and absorption and absorption of minerals was shown. This finding indicates that the changes in abundance of the commensal bacteria in the gut microbiome are capable of fermenting and using the carbohydrates that they’re ingesting, which increases the availability of minerals, and promotes absorption in the large intestine.4 Table 2 shows the two diets and what bacterial species would be expected to increase or decrease in each diet. Species that will increase have higher carbohydrate fermenting power, can produce butyrate, or are proteolytic. Butyrate is a short-chain fatty acid, a compound that provides energy to the intestinal epithelium and supports the immune system functions in the digestive tract. Butyrate breaks down fiber, which is a carbohydrate that the body can’t digest down into a sugar molecule like glucose, into energy that our dogs can use. The more butyrate that is produced, the more fiber that gets broken down, the more energy is provided to our dog. Proteolytic bacteria refer to those that produce proteolytic enzymes which are enzymes that break the bonds in protein molecules into amino acids that can be used for energy.
Food = Energy = Happy Pup.
Table 2: The expected increase and decreased in bacterial species per macronutrient change in diet.
Adapted from: Bartges, J. Gut Microbiome and Obesity. Hill’s Global Symposium, 2019.
While the dog gut microbiome is still being extensively researched, we do know the basics. Our dogs’ genetics, age, breed, weight, activity levels, and diet affect their gut microbiome composition. Most commercial kibble brands are high-carbohydrate (and therefore low protein), so we tend to see higher levels of Prevotella, Clostridium, Lachnospiraceae, and Ruminococcaceae species in the gut microbiome. While these bacteria are great at fermenting all those carbs that our dogs are consuming to meet their energy needs, it may also be an indicator of a macronutrient imbalance. Importantly, Prevotella is a versatile bacterium that can break down molecules both complex and simple. Knowing how your dog’s diet affects their microbiome and their body overall will allow you to make more tailored decisions on what you feed them.
References
1. Pilla S. The Role of the Canine Gut Microbiome and Metabolome in Health and Gastrointestinal Disease. Frontiers in veterinary science. 2019;6:498–498. doi:10.3389/fvets.2019.00498
2. Bartges, J. Gut Microbiome and Obesity. Hill’s Global Symposium, 2019.
3. Sanderson, S. Nutritional Requirements and Related Diseases of Small Animals. MERCK MANUAL Veterinary Manual. Merck Sharp & Dohme Corp. 2013.
4. Li L. Effects of the dietary protein and carbohydrate ratio on gut microbiomes in dogs of different body conditions. mBio. 2017;8(1):e01703–16-. doi:10.1128/mBio.01703–16