Your Dog's Second Brain
The gut has its own nervous system. It's called the enteric nervous system, and it contains roughly 500 million neurons, more than the spinal cord. This "second brain" can operate independently of the central nervous system, controlling gut motility, secretions, and blood flow without any input from the brain. But it doesn't operate in isolation. The gut and the brain are in constant communication through what scientists call the gut brain axis.
This connection means that what happens in your dog's gut doesn't stay in the gut. It influences mood, behavior, cognitive function, stress responses, and even the progression of neurodegenerative conditions. If you've ever noticed that your dog seems "off" when their stomach is off, you've observed the gut brain axis in action.
How the Gut Talks to the Brain
The Vagus Nerve
The vagus nerve is the primary physical highway between the gut and the brain. It's the longest cranial nerve in the body, running from the brainstem to the abdomen. Signals travel both directions: the brain sends information down to regulate digestion, and the gut sends information up about its internal state. Approximately 80% of vagus nerve fibers carry information from gut to brain, not the other direction. The gut is doing most of the talking.
Neurotransmitter Production
Gut bacteria produce neurotransmitters that influence brain function:
- Serotonin: Approximately 90% to 95% of the body's serotonin is produced in the gut. Serotonin influences mood, anxiety, and cognitive function. While gut produced serotonin doesn't cross the blood brain barrier directly, it influences the brain through vagus nerve signaling and through effects on gut inflammation and immune function that secondarily affect the brain.
- GABA: The primary inhibitory neurotransmitter (calming signal) in the brain. Certain Lactobacillus and Bifidobacterium species produce GABA in the gut.
- Dopamine: About 50% of the body's dopamine is produced in the gut. Dopamine influences motivation, pleasure, and reward processing.
Immune Signaling
The gut's immune cells (remember, about 70% of the immune system is gut associated) produce cytokines that can influence brain function. Pro inflammatory cytokines produced in response to gut imbalance can cross the blood brain barrier and affect neuroinflammation, contributing to anxiety, depression like behaviors, and cognitive decline.
Microbial Metabolites
Short chain fatty acids (SCFAs) produced by gut bacteria when they ferment dietary fiber have been shown to influence brain function. Butyrate, one of the primary SCFAs, has neuroprotective properties and supports the integrity of the blood brain barrier. Reduced SCFA production (from fiber poor diets or disrupted microbiome) may compromise brain health.
Gut Brain Connections in Dog Health
Anxiety and Stress
Studies in both dogs and other species have linked gut microbiome composition to anxiety behaviors. A 2019 study in dogs found that anxious dogs had different gut microbiome profiles compared to calm dogs, with reduced diversity and altered ratios of specific bacterial groups. While it's not yet clear whether the microbiome changes cause anxiety or anxiety alters the microbiome (likely both), the connection is robust.
Cognitive Function
Emerging research suggests that gut health influences cognitive aging. In a 2021 study published in Animal Microbiome, older dogs with signs of cognitive decline had different gut microbiome compositions compared to cognitively healthy dogs of the same age. The researchers hypothesized that gut derived inflammation and reduced production of neuroprotective metabolites contributed to the cognitive differences.
Behavior Changes
Dogs with chronic GI issues (food sensitivities, inflammatory bowel disease, dysbiosis) often exhibit behavioral changes that resolve when the gut issue is addressed. This includes increased irritability, reduced social engagement, altered sleep patterns, and changes in activity levels.
Supporting the Gut Brain Axis
Diet Quality
A diverse, fiber rich diet supports a healthy gut microbiome, which supports healthy gut brain communication. Adding dog safe fiber sources (pumpkin, sweet potato, green beans), fermented foods (plain kefir in small amounts), and varying protein sources promotes microbial diversity.
Probiotics
Specific probiotic strains have been shown to influence behavior and stress responses in dogs. Bifidobacterium longum BL999 was shown in a 2016 study to reduce anxious behaviors in dogs. Look for probiotics that contain strains with documented effects, not just generic "probiotic blend" products.
Prebiotics
Fructooligosaccharides (FOS) and other prebiotic fibers feed beneficial bacteria, promoting SCFA production and supporting the overall microbial ecosystem.
Bone Broth
Bone broth provides glutamine (which supports gut lining integrity), glycine (which has calming properties and supports the gut barrier), and other amino acids that nourish both the gut and the nervous system. This is one reason I appreciate the bone broth component in LongTails; it supports gut health alongside the NR for cellular energy.
Minimize Gut Disruptors
Unnecessary antibiotics, chronic NSAID use (which can irritate the gut lining), high stress environments, and poor quality food all disrupt the gut microbiome and can negatively impact the gut brain axis. Use medications when truly needed, but be aware of their gut effects and support recovery afterward.
The Implications for Aging Dogs
As dogs age, both gut health and brain health decline simultaneously, and they likely accelerate each other's decline. An aging gut produces less favorable metabolites, generates more inflammation, and has a less diverse microbiome. This compromised gut state then sends less supportive signals to an aging brain. Meanwhile, the aging brain sends less effective signals to the gut, further disrupting digestive function.
Breaking this cycle requires attention to both ends of the axis. Supporting gut health through diet, probiotics, and gut nourishing nutrients while simultaneously supporting brain health through mental engagement, cellular support, and anti inflammatory strategies gives the gut brain axis the best chance of functioning well into the senior years.
The next time you think about your dog's cognitive health, think about their gut too. And the next time you think about their digestion, consider how it's affecting their brain. They're one connected system, and supporting both is the path to a dog who ages with both a sharp mind and a settled stomach.
