When we think of the gut microbiome, we consider it mainly in terms of digestive health. But the truth is, the state of your dog or cat’s gut microbiome can affect other parts of his body, from his brain to his lungs.
Every surface of your dog or cat’s body (and your own) has a microbiome. However, the vast majority of microbial biodiversity is found in the nutrient-rich environment of the gastrointestinal tract. At least 200 times as many cells, and even more unique gene products, are found in the intestinal microbiome than in all the native cells of the body combined. So it should come as no surprise that what’s happening within your dog or cat’s gut microbiome can have an influence on other areas of his body, impacting everything from behavior to lung health.
Consequences of an Imbalanced Microbiome
1. Dysbiosis of Gut and Lungs
When the balance of beneficial and harmful microbiota (bacteria, viruses, fungi, parasites) in the intestines is disrupted by the process called dysbiosis, the result can not only affect the bowel but also the lungs. In some lung disease in humans and animals, in fact, the role of the intestinal microbiota exceeds that of the organisms residing in the lungs! Note that the dysbiosis can be present for years without obvious clinical symptoms.
Fast fact: Although the gut and lungs are distinct anatomical sites in the body, their microbiota still communicate via complex pathways within the gut–lung axis.
Study of the lung microbiota has begun only recently; while it mostly focused on bacterial content at first, it now also includes viral and fungal inflammatory effects. A key role has also been identified for inter-kingdom cross-talks in maintaining body homeostasis and in the evolution of disease. Inter-kingdom cross-talk refers to the ability of pathogens to sense their environment, influencing their capacity to survive and cause disease. This cross-talk involves host–microbe as well as microbe–microbe interactions, which have both localized and long-reaching effects.
2. Food Intolerances
With the growing number of individuals experiencing dysbiosis from an imbalanced microbiome, food intolerances are increasing, and many people have opted to reduce or exclude specific foods or have chosen to eat gluten-free and Paleo diets. The same trend is occurring among the dogs and cats in their care. Supporters of the gluten-free diet argue that gluten triggers inflammation and related diseases, while followers of the Paleo diet, which is free of all cereals, state that cereals are dangerous for human and animal health. They further argue that gluten-free cereals were absent in the diet of our ancestral hunters and gatherers, and the companion animals that foraged with them.
No placebo double-blinded controlled studies either support or reject the positive health impacts a gluten-free or cereal-free diet has on the gut microbiota of people or animals. Importantly, dogs have evolved from their wolf ancestors to become obligate omnivores. By contrast, cats remain primarily obligate carnivores and need some meat in their diet.
Fast fact: Dogs have adapted to domestication by developing three additional genes that allow them to digest and assimilate starch.
In obese people, eating high-protein diets changes the fecal microbiome composition to a less healthy state. In contrast, obese dogs produce different gut microbiota when eating high dietary protein, and lean dogs that consume higher protein diets show increased production of the fermentation products involved with putrefaction.
In a comparison of dogs fed high protein (HP) and those fed lower protein (LP), the HP dogs had higher concentrations of protein fermentation metabolites and plasma acylcarnitine. There were no observed changes in fecal concentrations of acetate and butyrate. Significant interactions between diet and body condition were also found. The similarity coefficient of fecal microbiota between the two diets was smaller in obese dogs than in lean dogs.
Aggression, a serious behavioral disorder in dogs, endangers both animals and humans. Recent research in humans has linked the compositional diversity of the gut microbiome to behavioral and psychological regulation. Thus, the composition of the canine gut microbiome could be associated with aggression.
Researchers studied pit bull-type dogs seized from a dogfighting organization, including 21 that displayed aggressive behaviors and ten that did not. Beta-diversity analyses supported an association between their gut microbiome structure and aggression. Gut microorganisms were linked to aggression and pointed to an aggression-associated physiological state that interacts with the gut microbiome. Further, microbial composition and levels differed based on the aggressive and non-aggressive evaluations. Eventually, studies of these and other dogs could be used to develop diagnostics, preventative strategies, and therapeutics for aggression.
Fast fact: Perhaps specific beneficial bacterial strains could be identified and used as probiotics to alleviate aggression.
4. Vaccination Response
Gut microbiota are also known to affect the response to vaccines. An imbalanced population of reduced or absent commensal gut flora coupled with an overgrowth of pathogenic gut flora is associated with systemic inflammation and a blunted immune response to vaccination. However, there are currently no published studies explaining how microbiota may also be associated with adverse reactions to vaccination.
As we learn more about the gut microbiome, we’re realizing what a profound effect it has, not just on digestive processes, but on many other facets of our health and well-being – and that of our animal companions.
W. Jean Dodds, DVM