How your dog’s gut microbiome affects his behavior

How your dog’s gut microbiome affects his behavior

Canine behavioral problems like anxiety and aggression can have many causes, and an out-of-balance microbiome may be one of them. Learn how your dog’s gut health can influence his behavior. 

If you’ve been learning about your dog’s (or your own) microbiome, you may be familiar with the term “gut-brain axis”. Several years ago, medical scientists suggested the gut was the “second brain” because so many of the neurotransmitters used by the brain and nervous system are created in the gut. However, the latest research suggests the enteric system (gut) may actually be viewed as the first or primary brain. That’s because gut health and microbes influence mental condition and behaviors such as aggression and anxiety (as well as immune function and overall health) in both humans and animals. Let’s take a look at how your dog’s gut health can impact his behavior.

Bacteria in the gut communicate with the brain

Gut bacteria make chemicals that communicate with the brain through the nerves and hormones — this connection is called the gut-brain axis. In fact, it is now known that many key chemicals and hormones used by the brain and nervous system, such as serotonin, dopamine and GABA, are produced in the gut.

  • Serotonin impacts mood and anxiety, and has actually been termed the “happy chemical” because it contributes to emotional well-being, while low levels of serotonin have been associated with depression. It is estimated that 70% of serotonin is made in the gut.
  • Dopamine is involved in motor function, mood, decision-making, and the control of other hormones. Reports estimate that about 50% of dopamine is produced in the gastrointestinal tract by enteric neurons and intestinal cells.
  • GABA regulates stress, anxiety and sleep patterns, and is known to be modulated by bacteria in the gut microbiome.

To be clear, “microbiome” is the term used to describe the vast ecosystem of bacteria, fungi and viral organisms that live within the bodies of all other living organisms, including you and your dog. Our microbe populations actually far exceed the number of our cells. In fact, the number of microbial organisms living in just the intestinal environment is ten times greater than the number of cells in the host’s body! Everybody’s microbiome is essentially like a fingerprint, unique to the individual, but animals within the same species will have many similarities. The more diverse the microbiome is, the healthier the person or animal will be!

Behavioral issues are part of the scenario

A recent blog from Animal Biome states: “clinical studies are finding that gut bacteria send important chemical messages to the brain, and these chemical messages can have a big impact on one’s mood”.

These effects depend on which bacteria are in the gut, because different species make different chemicals. Certain bacteria make chemicals that have a calming effect, while others may promote depression and anxiety.

Animal Biome offers fecal testing to analyze the microbiome status of dogs (and cats). I frequently recommend this type of testing for my patients, and the results often show a moderate to significant gut bacteria imbalance. Known as a dysbiosis, this imbalance is an underlying factor in many gastrointestinal diseases such as IBD, as well as systemic body problems like allergies. If a dysbiosis is identified, a fecal transplant treatment offers excellent therapeutic potential for repopulating the animal’s gut with good microbes, ultimately bringing his gut function and immune system into better balance.

This type of testing and treatment is gaining more attention in the veterinary field, but its focus so far has been on disease issues related to the gut or immune system. However, new research may have us looking at fecal testing and transplant treatment for behavioral disorders as well.

The link between canine aggression and gut microbes

A new groundbreaking study at the University of Oregon shows a clear link between aggressive behavior in dogs and the microbes that live in their guts. The study analyzed a population of similar-breed rescued dogs in a shelter setting, and compared evaluations of behavior with microbiome status via a series of fecal tests. While this study could not distinguish the exact relationship between cause and effect, it reveals that the gut microbiome may contribute to aggression or its severity, and that manipulation of the microbiome, via probiotics or dietary changes, may modify behavior.

The results also suggest that analyzing the canine gut microbiome may have some predictive value in the diagnosis of aggressive behavior conditions. However, it is not yet fully understood if both aggressive behavior and the gut microbiome are similarly affected by other variables such as inflammation or cortisol levels (which are elevated by chronic stress).

Another recent study, reported in Science Direct (January 2020), evaluated gut microbiome and adrenal gland activity in dogs with aggression and fear-related behavioral issues. The study evaluated the connections between the dog’s gut microbiome and the central nervous system, and discussed the potential for using probiotic interventions aimed at restoring a balance for mitigating behavioral disorders. The researchers also found that long-term stress scenarios do influence gut microbiome composition. More research is needed to decipher the precise cause and effect relationships between canine behavioral disorders and the gut microbiome.

Modern food production practices damage the microbiome

The microbiome’s diversity and balance determine much of the body’s gut function, immune system status, brain function, and even patterns of inflammation. A healthy microbiome depends on many factors – the type of diet and daily nutrients ingested, antibiotic exposure, leaky gut versus healthy gut, etc.

Antibiotic exposure is of huge concern. The use of antibiotics in the production of food animals greatly exceeds the known overuse of antibiotics in the medical industry (prescription medications). Added to that, we have the use of Monsanto’s Round-Up, which is technically an antibiotic as well as a weedkiller. These modern day practices are depleting and/or causing an imbalance in the microbiomes of both people and their dogs.

We now understand that heavily processed foods (i.e. those treated with extreme or high heat) along with the toxins in many foods, are causing gut inflammation and leaky gut syndrome, and altering the gut microbiome. New research points to the significance of high carbohydrate diets (which break down into sugars in the body), and how they are affecting the microbiome, when compared with evolutionary-appropriate meat-based diets.

In short, highly processed pet foods — i.e. heavily-heated foods with more carbohydrates than dogs were designed to eat, along with antibiotics and toxins in the ingredients – are negatively affecting microbiome status and overall health.

Dietary intervention may modulate behavior

These new findings contribute to a better knowledge of the mechanisms that connect gut microbiota and behavior, and how problem behaviors in dogs may be affected by dietary means. The Science Direct study concluded that, “ultimately, this type of research provides insights into veterinary behavioral medicine, which may help to develop a predictive diagnosis of canine behavioral disorders”.

Other research has looked at how dietary interventions can modulate anxiety and depression behaviors. Findings published in Science Direct (January 2017) demonstrated that the addition of DHA (i.e. Omega-3 fatty acids, such as those in fish oils or cod liver oil) produced a beneficial effect on behavior, apparently through the action of altering the community composition of bacteria in the body.

Molecular Psychiatry (April 2016) reported “the gut micbrobiome is an increasingly recognized environmental factor that can shape the brain through the microbiota-gut-brain axis”. This particular study demonstrated that dysbiosis may have a causal role in the development of depression behaviors. This is validated by another study (PNAS 2011)

which found that ingestion of a particular Lactobacillus probiotic strain regulated emotional behavior, due to its effects on the production of GABA. These findings introduced the opportunity for developing unique microbial-based strategies for the treatment of stress-related disorders.

In summary, there is growing interest in the connection between behavior in dogs and their diets, gut health and microbiome status.

“While I recommend working with a behavioral trainer on issues of aggression and anxiety, we have seen many cases of improved behavior after the rebalancing the gut microbiome,” says microbial ecologist and Animal Biome founder, Holly Ganz, PhD.  “I am excited and encouraged by the current research into the relationship between the gut microbiome and behavior, and am optimistic that manipulations of the microbiome through diet and fecal transplants may one day help manage anxiety or aggression in companion animals.”

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