If This Were a Horse, You’d Say Ulcers.

Why We Acknowledge the Gut-Brain Axis in Horses — But Not in Dogs

As a horse person, I’ve seen it over and over: A horse starts acting out — girthy, grumpy, hard to settle — and the first thing someone says is: “Maybe ulcers?”

Gut discomfort is one of the first places equestrians look when a horse’s behavior changes. But in the dog world? We rarely talk about it at all.

Instead, we label dogs “reactive,” “disobedient,” or “stubborn.” We throw food at them for training. Or worse, we try to “exercise the energy out.” And we completely miss what’s happening inside.

It’s time we started talking about the gut-brain axis in dogs, not in a trendy way, but in a real, physiological, behavior-shaping way.

What Is the Gut-Brain Axis?

The gut is lined with nerves, over 100 million neurons in the enteric nervous system (ENS), often called the “second brain.”

This system talks directly to the brain via the vagus nerve, and helps regulate:

• Emotional stability

• Focus and learning

• Sensory processing

• Sleep and recovery

• Hormonal and immune responses

In fact, around 90% of the body’s serotonin is produced in the gut, by specialized cells that interact with the microbiome.

This serotonin doesn’t cross into the brain directly — but it shapes how the brain works by:

• Influencing inflammation

• Regulating gut motility and digestion

• Affecting cortisol and stress hormones

• Modulating dopamine and GABA levels

In short?

If the gut isn’t safe, the brain isn’t stable. And your dog’s behavior starts to show it.

What Gut Dysregulation Looks Like in Dogs

We tend to recognize diarrhea and vomiting as gut issues. But that’s just the tip of the iceberg.

Dysbiosis (an imbalanced gut microbiome), leaky gut, or chronic inflammation can show up as:

• Pacing or restlessness

• Barking or reactivity “for no reason”

• Trouble sleeping or settling

• Hypervigilance

• Scavenging, air licking, or constant hunger

• Inconsistent stools or gurgly belly

• Overreactions to normal sounds or triggers

These dogs aren’t being bad. They’re dysregulated.

Grady’s Story: From Cell-Level Chaos to Sparkle

After mold exposure, my dog Grady spent nearly a year in a state of desperate hunger, emotional fragility, and digestive instability. He wasn’t misbehaving — he was malabsorbing. His gut lining was damaged. His microbiome was out of balance. His nervous system couldn’t stabilize.

We had to rebuild his health from the inside out — spoonful by spoonful. We paused activity during reintroductions. We added fats one at a time. We tracked his “sparkle” — that little glimmer of energy, joy, and restfulness, because sparkle was our sign that digestion was working.

Grady wasn’t just recovering behaviorally. He was reestablishing cellular safety.

And that made all the difference.

Why It Matters

If you wouldn’t dismiss your horse’s tension or resistance…If you’d call the vet to rule out ulcers…Then maybe it’s time to ask the same questions for your dog.

Your dog’s behavior is never “just behavior.” It’s information. And when you understand the gut-brain connection, you start to see what they’re really telling you.