The Microbiome

Independent Research: Gut Microbiota and Anxiety in Companion Dogs

A 2025 peer-reviewed study of 48 companion dogs examined whether gut microbiota composition was associated with owner-reported anxiety and aggression. Although simple abundance differences between behavioural groups were limited, machine-learning and compositional models could distinguish higher- and lower-anxiety dogs from microbiome data, with Blautia repeatedly identified as an important genus.

Peer reviewed Open access

Independent Research: Gut Microbiota and Anxiety in Companion Dogs

Year

2025

Study type

Peer-reviewed observational study

Sample

48 companion dogs

Measured

Faecal microbiota composition, anxiety scores and aggression scores

The research question

Research in several species has suggested a relationship between the gut microbiome and behaviour.

But in companion dogs, that relationship is still not well understood.

Pellowe and colleagues investigated whether dogs with different levels of owner-reported anxiety and aggression also differed in their gut microbiota.

The central question was:

Can the composition of the faecal microbiota distinguish dogs with higher behavioural anxiety or aggression scores from dogs with lower scores?

This was an observational study.

The researchers did not change the dogs' microbiomes or behaviour experimentally, so the study was designed to identify associations rather than demonstrate cause and effect.

What did the researchers do?

Dog owners first completed questionnaires covering their dogs' diet, lifestyle and medical history.

Behaviour was assessed using the Canine Behavioral Assessment & Research Questionnaire, commonly known as C-BARQ.

Dogs received composite scores for anxiety and aggression.

The anxiety score incorporated measures including:

Dog-directed fear

Stranger-directed fear

Nonsocial fear

Separation-related problems

The aggression score incorporated:

Stranger-directed aggression

Owner-directed aggression

Dog-directed aggression

Dogs were divided into higher- and lower-scoring groups.

After matching and filtering, faecal samples from 48 companion dogs were included in the microbiome analysis.

Microbial DNA was extracted from the samples and sequenced.

The researchers then used several statistical approaches, including compositional analyses and machine-learning models, to investigate whether microbiome patterns could distinguish the behavioural groups.

What did they measure?

The study examined several layers of microbiome data.

Bacterial relative abundance

Researchers compared the proportions of different bacterial groups between higher- and lower-anxiety and aggression groups.

Microbial diversity

Measures of within-sample diversity were compared between behavioural groups.

Compositional balances

Rather than considering individual bacteria in isolation, the researchers examined relationships between groups of bacteria.

Machine-learning classification

Models were trained to determine whether microbiome composition could predict whether a dog belonged to the higher- or lower-anxiety or aggression group.

Specific taxa

The analysis investigated which bacterial groups contributed most consistently to differences between behavioural categories.

What was observed?

The results were more nuanced than simply finding one set of bacteria in anxious dogs and another in non-anxious dogs.

Simple abundance differences were limited

After correction for multiple statistical comparisons, broad differences in individual bacterial abundance and diversity between groups were relatively small.

Microbiome patterns nevertheless contained behavioural information

When researchers considered relationships across the microbial community, the microbiome could distinguish higher- and lower-anxiety groups.

A compositional model based on the balance between Blautia, Oscillospiraceae and Negativicutes achieved an AUC-ROC of approximately 0.86 for classifying higher- and lower-anxiety dogs.

Machine learning produced a similar result

The best-performing machine-learning model for anxiety achieved an AUC-ROC of approximately 0.87.

This means the overall microbial pattern contained meaningful information about which behavioural group a dog belonged to.

Blautia appeared repeatedly

The genus Blautia was identified across several different analytical approaches and showed a particularly consistent relationship with anxiety.

Higher-anxiety dogs tended to have greater Blautia relative to some other microbial groups.

Aggression produced a weaker signal

Microbiome models could also distinguish higher- and lower-aggression dogs, but performance was lower than for anxiety.

The best aggression model achieved an AUC-ROC of approximately 0.73.

What does this study tell us?

This study adds to evidence that canine behaviour and the gut microbiome are related.

Its most interesting finding is not that one particular bacterium can explain anxiety.

It is that patterns across the microbial community contained enough information to distinguish dogs with higher and lower anxiety scores.

That supports the idea that behaviour may be associated with the broader gut ecosystem rather than with a single microorganism.

The repeated identification of Blautia is scientifically interesting, but it should be interpreted carefully.

Blautia contains multiple species and strains, and the biological role of the genus cannot be inferred from relative abundance alone.

The researchers themselves emphasised that additional metagenomic and metabolomic work would be needed to understand what these organisms were actually doing.

The study therefore supports an association:

Microbiome composition ↔ Behavioural phenotype

It does not establish:

Microbiome composition → Anxiety

That distinction is critical.

For the broader biology of gut and brain communication, read our canine gut-brain axis explainer.

A separate study asked whether acute stress changed gut microbiota in dogs and reported its methods and limitations.

What doesn't this study tell us?

The authors identify several important limitations.

Observational design

The study measured microbiome composition and behaviour at the same time.

It cannot establish whether microbial differences influenced behaviour, behaviour influenced the microbiome, or both were influenced by another factor.

Behaviour was owner reported

C-BARQ is an established behavioural assessment tool, but the results still depend on owner observations rather than blinded behavioural testing.

Relatively modest behavioural severity

Many dogs had relatively low anxiety and aggression scores.

The authors suggest that future studies should include larger numbers of dogs with more pronounced behavioural problems.

Diet was not fully controlled

The study attempted to match dogs for several important factors, but participants remained community-owned pets eating different diets.

Diet itself can strongly influence microbiome composition.

Sample size

Forty-eight dogs were included in the microbiome analysis.

This is useful for exploratory research but remains relatively small for complex machine-learning analyses.

16S sequencing has limited functional resolution

The study primarily examined microbial composition.

It could not determine microbial function directly or reliably identify every organism to species level.

The authors specifically recommend future metagenomic and metabolomic work.

For these reasons, the results should be viewed as evidence of association rather than evidence that altering a particular bacterial group will change anxiety or aggression.

Original research

Study details

Study

Gut microbiota composition is related to anxiety and aggression scores in companion dogs

Authors

Sarita D. Pellowe
Allan Zhang
Dawn R. D. Bignell
Lourdes Peña-Castillo
Carolyn J. Walsh

Institutions

Memorial University of Newfoundland, Canada

East Coast Canine Dog Training, Canada

Reference

Pellowe SD, Zhang A, Bignell DRD, Peña-Castillo L, Walsh CJ. Gut microbiota composition is related to anxiety and aggression scores in companion dogs. Scientific Reports. 2025;15:24336.

Published 8 July 2025.

The study analysed faecal microbiota from 48 companion dogs and compared microbiome composition with anxiety and aggression scores derived from the Canine Behavioral Assessment & Research Questionnaire.

DOI: 10.1038/s41598-025-06178-4

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