When your dog reacts to another dog, pulls, barks, or freezes — you're seeing the end point. But that reaction started much earlier, deep inside the body. To understand why some dogs are so quick to switch "on," you have to follow the path from stressor to hormone to gut.
Step by step: what happens in the body
Another dog, an unfamiliar sound, a busy street — the brain registers danger. It doesn't have to be real danger. For a dog with a sensitive nervous system, the perception is enough.
The hypothalamus sends the signal: danger. The adrenal glands release cortisol — the primary stress hormone. The body shifts into fight-or-flight. Muscles tense, heart rate climbs, digestion is temporarily put on hold.
Acute stress is fine. But with chronic stress, cortisol circulates continuously — and that has a direct effect on the gut lining. Permeability increases, the bacterial population shifts, and the gut environment becomes disrupted.
Under chronic stress conditions, the presence of bacteria that produce short-chain fatty acids declines. Blautia is one of them — a genus that plays a role in inflammation regulation and gut-brain communication. Recent research found that dogs with higher anxiety scores had an altered Blautia profile.
More than 90% of the body's serotonin is produced in the gut — not the brain. Serotonin regulates mood, impulse control, and the threshold for stress responses. Fewer of the right gut bacteria means fewer serotonin precursors, and therefore a lower buffer against stress.
With less serotonin, a dog has less room to stay calm. The same situation he could handle before now becomes too much. He reacts sooner, harder, and is harder to interrupt. From the outside it looks random. From the inside, it's physiology.
The cycle that keeps itself going
Every loop through that cycle makes it harder to break. Not because the dog doesn't want to learn — but because his physiology keeps him in a constant state of readiness.
What the research confirmed
In 2025, researchers at Memorial University (Canada) published a study in Scientific Reports that was among the first to systematically investigate this link in companion dogs. They used the C-BARQ — a standardized behavioral questionnaire — to sort dogs by anxiety and aggression levels. They then analyzed each dog's gut microbiome composition through DNA sequencing of fecal samples.
Machine-learning models could correctly predict which behavioral group a dog belonged to based on that microbiome composition. And Blautia — the genus from step 4 — came up consistently as a distinguishing factor in anxious dogs.
What you might do with it — food and bacteria
As a next step, the researchers hope to investigate whether probiotics have a positive effect on anxious behavior in dogs. That research is still underway. What we do already know: the gut microbiome responds to food, stress, and routine.
Fibers that support short-chain fatty acids — like those found in vegetables, certain grains, and fermented foods — give bacteria like Blautia the building blocks they need. Reducing chronic stress, keeping regularity in feeding and exercise, and avoiding unnecessary stress spikes: those are the levers already available today.
That's why an intake at Pawsitive Steps always starts broader: nutrition, daily structure, sleep patterns, activity level, stress history. Not because we're veterinarians — we aren't — but because behavior never exists in a vacuum.