Laura Ward
Pet Nutritionist


Gut health is a topic which has gained a lot of attention in recent years, in humans as well as dogs. There have been many studies researching how gut health impacts wider health and well-being. Before discussing these findings, lets start at the beginning.

What is the Microbiome?
You may have heard of the microbiome, but not be sure what it is and how it connects with the digestive system.

The microbiome is composed of a massive population of varied microorganisms which live within the gastrointestinal tract. Every individual dog has a unique microbiome and studies have found many factors affect the microbiome population, from age, breed, and neuter status to body condition score. The quantity of microbes in both numbers and species increases with progression through the digestive tract, from the small to large intestine, where the largest proportion of the microbiome resides. The microorganisms of a dog’s digestive tract even outnumber that of the human gut!

The biggest part of the microbiome is the bacteria. They are responsible for fermentation of fibre within the large intestine and other digestive functions. Knowledge of the gut microbiome and its functions and interactions is growing, and it is now known that the microbiome effects metabolism and immunity.

Response to Diet
The gut microbiome responds to nutrients in the diet. Bacteria in the microbiome are varied, some species ferment fibres, others digest proteins, and so on. Changes to the macronutrient profile of the diet change the availability of nutrients in the gut and therefore cause changes to the microbiome population. The microbiome is resilient, and therefore these adjustments are only sustained for as long as the dietary change is maintained. Once the diet returns to the previous norm, the microbiome population also returns to its default. For example, if you switch your dog’s food to one containing higher protein, the microbiome population will adjust to this new abundance of protein. Once your dog’s food returns to normal, the extra microbiome capacity to handle these extra proteins will also return to what it was previously. The macronutrients of a canine diet are seen to have a greater impact on microbiome populations that changes to dietary ingredients. Therefore, if the ingredients within your dog’s diet vary, but the resulting protein, fat and fibre quantities within the diet are stable, the microbiome is less affected than if the ingredients remain constant and the analysis of the diet changes.

Prebiotic fibres can support the recovery of “good” bacterial species of the microbiome. Including prebiotics within canine diets can improve gut microbiota and the health of the digestive tract.
Probiotics are fed to support recovery. Bacterial population in the microbiome which come from probiotics are often short-lived, but whilst they reside within the gut they are active and can provide benefits to relieve symptoms of digestive upset.

Probiotics have been shown to have protective effects against issues of acute diarrhoea in dogs and improving recovery time from chronic diarrhoea. This is therefore a proven method to promote and sustain optimal digestive health of dogs, but dietary probiotics have even wider ranging effects. When probiotics are provided to young dogs improvements to their immune function are seen, showing probiotics form a protective measure for immune responses during the critical weaning period continuing into later growth.

Health and Disease
There are many microorganisms which occupy the same functional space or do the same job within the microbiome. This means that any issue damaging one microorganism species (such as a course of antibiotics) would not stop the whole microbiome. As multiple species are required for this resilience of the microbiome, higher species richness is an indication of a healthy microbiome.
Disease also affects microbiome populations. Microbiome diversity is reduced in dogs which are unwell, especially in the case of gastrointestinal illnesses. Gut Dysbiosis “a change in the composition of the gut microbiome that impacts its function” is related to many areas of health and disease, from immunity to obesity and cancer.

Microbiome Communication
Studies have shown the capability of the mammalian gut microbiome to communicate with the central nervous system through multiple signals, channels, and other methods. These various signals form the gut-brain, gut-skin and gut-immune axes. These axes are two directional! The central nervous system can influence the gut microbiome and the gut microbiome can influence the central nervous system, showing that the gut microbiome can affect behaviour. This influence can affect the gut environment, as well as motility, secretion, and gut permeability. The two-directional nature of the gut-brain axis (and the other axes) shouldn’t come as a surprise, as we have all experienced these effects. Think about how eating badly makes us feel lethargic and how stress can cause upset digestion.

In summary, gut health is a key focus to maintaining good overall health and wellbeing in our dogs. Studies are revealing more about communications with the gut microbiome and other areas of the body, such as the brain-gut axis. There is so much to learn about the microbiome, which is even considered an organ in its own right! We do know that maintaining good gut health is a priority to maintain healthy and happy dogs.


1) Mondo E, Barone M, Soverini M, D’Amico F, Cocchi M, Petrulli C, Mattioli M, Marliani G, Candela M, Accorsi PA. Gut microbiome structure and adrenocortical activity in dogs with aggressive and phobic behavioral disorders. Heliyon. 2020 Jan 29;6(1):e03311. doi: 10.1016/j.heliyon.2020.e03311. PMID: 32021942; PMCID: PMC6994854.
2) Craddock, Hillary & Godneva, Anastasia & Rotshchild, Daphna & Motro, Yair & Grinstein, Dan & Lotem-Michaeli, Yuval & Narkiss, Tamar & Segal, Eran & Moran-Gilad, Jacob. (2022). Phenotypic correlates of the working dog microbiome. npj Biofilms and Microbiomes. 8. 66. 10.1038/s41522-022-00329-5.
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