The Microbiome

The Gut-Brain Axis in Dogs: How the Gut and Brain Communicate

The gut and brain communicate continuously through nerves, hormones, immune signalling and microbial metabolites. This two-way network, known as the gut-brain axis, helps explain why changes within the gastrointestinal environment can be associated with changes in stress, behaviour and overall neurological signalling.

Science explainer

The Gut-Brain Axis in Dogs: How the Gut and Brain Communicate

Content type

Science explainer

Focus

Neural, endocrine, immune and microbial communication between the gastrointestinal tract and brain

The big question

The digestive system and the brain are not isolated organs.

They communicate continuously.

Signals travel from the brain to the gastrointestinal tract, influencing processes such as motility, secretion and appetite.

At the same time, information from the gut travels back towards the nervous system.

Microorganisms living within the gastrointestinal tract can also influence this communication by producing metabolites and interacting with immune and intestinal cells.

This interconnected system is known as the gut-brain axis.

The big question is:

How can events within the gut influence signals reaching the brain, and how can the brain influence what happens in the gut?

How do scientists study it?

Researchers study the gut-brain axis through several different biological pathways.

The nervous system

The gastrointestinal tract contains its own extensive network of neurons, known as the enteric nervous system.

Signals can also travel between the gut and brain through autonomic nerves, including the vagus nerve.

Hormonal signalling

The digestive tract produces numerous signalling molecules and hormones in response to food, nutrients and other stimuli.

These can influence appetite, metabolism and nervous-system activity.

Immune signalling

The intestinal lining contains a large immune network.

Microbial compounds, dietary molecules and changes in barrier function can influence immune signalling, which can in turn affect communication with the nervous system.

Microbial metabolites

Gut microorganisms transform dietary substrates into a wide range of metabolites.

These include short-chain fatty acids and many other compounds capable of interacting with intestinal, immune and neural pathways.

Behavioural studies

Researchers can compare microbiome or metabolite patterns with observable behaviour, stress responses or physiological measures.

These approaches help scientists investigate associations between the gut environment and behaviour, although they do not automatically prove cause and effect.

What can we measure?

Several major communication routes are repeatedly studied.

The vagus nerve

The vagus is one of the principal neural connections between the gastrointestinal tract and brain.

It carries information in both directions.

Signals generated within the gut can therefore influence nervous-system activity without requiring a microbial metabolite to enter the brain directly.

The enteric nervous system

The gut contains a large network of neurons embedded within the gastrointestinal wall.

This system helps regulate intestinal movement, secretion and local digestive activity.

It also communicates with the central nervous system.

Short-chain fatty acids

Acetate, propionate and butyrate are produced when microorganisms ferment certain substrates.

These metabolites can interact with intestinal cells, immune pathways and neural signalling.

Neuroactive compounds

Microbial communities can influence the availability or metabolism of compounds involved in nervous-system signalling.

However, detecting a neurotransmitter-related compound in the gut does not mean that it simply travels directly into the brain.

The hypothalamic-pituitary-adrenal axis

The HPA axis is a major component of the body's stress-response system.

Gut microbial signals and stress physiology can influence one another, creating a two-way relationship between gastrointestinal and neurological state.

Immune mediators

Inflammatory and immune signals provide another route through which events in the gastrointestinal tract can affect wider physiology.

What have we learned?

The gut-brain axis is best understood as a network rather than a single pathway.

Several important principles have emerged from the wider research.

Communication is bidirectional

Stress can alter gastrointestinal motility, secretion and microbial communities.

At the same time, changes within the gastrointestinal environment can alter signals travelling back towards the nervous system.

The microbiome can contribute to signalling

Microorganisms produce metabolites and interact with intestinal and immune cells.

These interactions provide plausible biological routes through which the microbiome can influence the wider gut-brain network.

Short-chain fatty acids are important signalling molecules

Butyrate, acetate and propionate are not simply waste products of fermentation.

They participate in intestinal, metabolic and immune signalling and are increasingly studied within gut-brain research.

Behaviour and microbiome composition can be associated

Canine studies have reported associations between microbial patterns and behavioural traits including fear, sociability and working-dog behaviour.

These findings are scientifically interesting, but associations alone do not demonstrate that changing a bacterial group will change behaviour.

Stress can also alter the gut

The relationship runs both ways.

Environmental stress and neurological state can influence digestion, gut motility and microbial ecology.

The gut-brain axis is therefore a feedback system rather than a one-directional pathway.

Why does this matter?

The gut-brain axis provides a biological framework for understanding why gastrointestinal and behavioural observations can sometimes occur together.

It does not mean that every behavioural change originates in the gut.

Nor does it mean that changing the microbiome will automatically change behaviour.

Instead, the science tells us that the digestive system, microbiome, immune system and nervous system are connected through several overlapping communication pathways.

This also links the gut-brain axis back to digestion.

The substrates reaching the microbiome influence microbial metabolism.

Microbial metabolism influences the compounds present within the gut.

Those compounds can interact with intestinal, immune and neural signalling.

A simplified pathway is therefore:

Digestion → Substrate availability → Microbial activity → Metabolites → Gut-brain signalling

This is one reason it is useful to study digestion, microbiome composition, metabolomics and behaviour together rather than as completely separate subjects.

For practical guidance when an individual dog seems anxious, read our guide to behaviour and gut health.

For a canine study examining associations between microbiota and behaviour, read the independent anxiety research.

What should we keep in mind?

Gut-brain research is a rapidly developing field, and several cautions are important.

Association is not causation

Finding a particular bacterial pattern in dogs with a behavioural characteristic does not prove that those bacteria caused the behaviour.

The system works in both directions

Stress can change the gut just as changes within the gut may influence stress-related signalling.

This makes cause and effect difficult to separate.

Human and rodent research cannot simply be transferred to dogs

Much of the detailed mechanistic work in this field comes from laboratory animals or human research.

Canine-specific evidence is growing but remains more limited.

Microbial metabolites have many functions

Compounds such as short-chain fatty acids participate in multiple biological processes.

Their presence should not be interpreted as evidence of one specific neurological outcome.

Behaviour is complex

Genetics, previous experience, learning, environment, pain, health, social factors and many other influences contribute to canine behaviour.

The microbiome is one potential component within a much larger biological system.

For these reasons, the gut-brain axis is best regarded as an important research framework rather than a simple explanation for behaviour.

Sources and further reading

References

Further reading:

Mondo E, Barone M, Soverini M, et al. Gut microbiome structure and adrenocortical activity in dogs with aggressive and phobic behavioral disorders. Heliyon. 2020;6(1):e03311.

Craddock HA, et al. The gut microbiome of working dogs is associated with behavioural and performance traits. npj Biofilms and Microbiomes. 2022.

Pilla R, Suchodolski JS. The Gut Microbiome of Dogs and Cats, and the Influence of Diet. Veterinary Clinics of North America: Small Animal Practice. 2021;51(3):605–621.

Cryan JF, O'Riordan KJ, Cowan CSM, et al. The Microbiota-Gut-Brain Axis. Physiological Reviews. 2019;99(4):1877–2013.

Related science

Continue exploring the science

CaniNectar Research

CaniNectar Research: Two-Phase Professional Field Trial

A two-phase professional field trial involving 129 dogs and 63 UK veterinary professionals, trainers and behaviourists examined real-world observations during CaniNectar use. The study included digestive, stool and behavioural measures across two independently run phases.

Read article →

CaniNectar Research

CaniNectar Research: UK Border Force Working Dog Trial

A four-week field trial in nine UK Border Force working dogs explored changes observed while dogs received CaniNectar, including stool quality, appetite and faecal microbiome composition. The study provides useful real-world observations alongside important limitations.

Read article →

CaniNectar Research

CaniNectar Research: Blue Cross Rescue Dog Trial

An independent four-week observational study conducted with Blue Cross followed 25 rescue dogs across three cohorts. Assessments included stool quality, behaviour and focus, skin condition and tolerability, with 24 dogs completing the study.

Read article →

Related health guides

Practical information for dog owners

The Gut & Behaviour

The Gut–Brain Axis in Dogs: What Do We Actually Know?

The gut and brain communicate through several biological pathways, including nerves, hormones, immune signalling and microbial metabolites. Research in dogs is growing, but the evidence is still developing and should be interpreted cautiously.

Read guide →

Scientific transparency

Microbiome science is complex and continually developing. Our Science Hub aims to explain the evidence clearly without presenting uncertainty as certainty.

← Back to Science Hub Explore the Health Hub →