The canine ‘gut microbiome’ refers to the incredibly diverse community of bacteria, fungi, viruses, and other microbes or microorganisms that live in a dog's gastrointestinal (GI) tract, or gut. And it’s not just about bacteria; it turns out many viruses are essential to health too.
But firstly; the gut comprises the entire intestinal tract, beginning in a dog’s mouth, and ending at
their anus. And it turns out, the gut is responsible for innumerable functions,
not simply digesting food. Research shows the canine gut microbiome is very
closely related to ours [1] and we also share
microbes with our companions. Sharing our homes with dogs (and cats) is
great for pet parents’ microbiome health, too.
These microscopic critters have co-evolved with our dogs, helping
to optimise food digestion, regulate the immune system, mood, and even produce
essential vitamins, such as B vitamins and vitamin K.
The Emerging
Science of the Gut-Brain Axis
That feeling of ‘butterflies in your stomach’ when you’re nervous?
Feeling ‘sick to your stomach’ when you hear bad news? Having a ‘gut feeling’
about something? All of this, in humans, is now being attributed to a very real connection [2] between our
microbiome and brain. The gut microbiome influences the development of the
brain and are now implicated, in humans, in numerous neurological diseases,
including dementia, and conditions such as depression, anxiety, autism, and bipolar disorder.
The same goes for our dogs.
The interaction between the microbiome and the brain is
facilitated several ways, involving neural connections via the vagus nerve,
immune system pathways, and specific chemicals produced by gut bacteria, called
metabolites.
Let’s define the canine microbiome in greater detail.
Composition
of the Canine Microbiome
Dogs harbour distinct microbiomes throughout their
body, varying with location, e.g.: ear canal, skin, respiratory tract, urinary
tract, and gut, etc. Most studies in dogs have centred the gut microbiome,
though it’s critical to keep in mind that other microbiome populations
throughout the body have
impacts on health. [4]
The composition of the canine microbiome varies
according to a dog's genetics, sex, age and diet, environment, medications,
and general health.
When present in a harmonious balance, healthy microbes promote
wellbeing, though when the microbiome is out of kilter, this is called
‘dysbiosis.’ Dysbiosis is associated with numerous canine diseases, ranging
from intestinal disorders, skin
issues, obesity, arthritis, and behavioural
problems.
That said there is a little bit of a ‘chicken and egg’ element here: is the microbiome unbalanced before the disease begins, or does the
disease cause dysbiosis? Or is it a
bit of both?
The microbiome has fundamental roles in:
#1. Digestion and
Nutrient Absorption
Microbes break down dietary fibres, resistant starch and proteins that are otherwise indigestible for dogs. This process produces compounds, called short-chain fatty acids (SCFAs) that nourish the gut cells, maintaining the health and integrity of the intestinal lining.
These SCFAs are also neuroprotective, promoting
brain health.
#2. Regulation of
the Immune System
The microbiome trains the immune system to recognise pathogens, whilst ignoring healthy microbes, harmless substances, and the body’s own cells. The microbiome prevents allergies and autoimmune diseases developing. An abnormal immune response towards healthy gut bacteria is implicated in inflammatory bowel disease. [7]
Dogs with
this condition typically have microbiome dysbiosis and faecal microbial
transplants (FMT), where faeces from healthy dogs is transplanted into the
intestines of dogs with chronic
gut disease, is becoming a routine, effective treatment. (In fact, FMT
is being explored
in
clinical trials for a myriad of human illnesses).
In dogs, FMTs use non-obese donors, as amazingly, faeces
from obese dogs causes obesity in recipients.
#3. Integrity of
the Gut Barrier
The lining of
the gut acts as a barrier between foreign materials (such as toxins, bacteria,
food allergens etc.) and the blood. During digestion, beginning in the mouth
and ending with the excretion of waste products, as faeces, only certain
substances should be absorbed by the intestines.
A balanced microbiome maintains the integrity of this barrier, the so-called gut mucosal barrier.
Disruption of this barrier, by certain compounds, pathogens, and an abnormal microbiome increases the permeability of the gut lining. This is sometimes referred to as ‘leaky gut syndrome’. Increased permeability allows harmful substances and microbes direct access the blood stream, causing widespread inflammation and numerous disease conditions.
#4. Production of
Neurotransmitters
Some of the microbes in the gut produce neurotransmitters, the
chemical messengers regulating mood, behaviour, appetite, and sleep. More than
90%
of the body’s ‘happy’ neurotransmitter, serotonin, is produced in the gut.
Certain types of gut bacteria produce γ-aminobutyric
acid, or ‘GABA,’ which has a
calming impact on the brain. Other neurotransmitters, involved in the ‘fight or
flight’ response, and other body functions are also
produced in significant quantities by the microbiome.
The microbiome has a significant impact on a dog’s memory and ability to learn as they age.
Certain canine phobias and aggressive behaviour have been linked to high levels of particular bacteria, and modulation of the microbiome is being investigated as a treatment modality in behavioural disorders. Research has identified microbiome associations in canine epilepsy and auto-immune disorders affecting the canine brain.
#5. Vagal Nerve
Communication
The vagus nerve is the major ‘super-highway’ between the gut and
the brain. Some gut
bacteria stimulate this nerve directly, sending signals to the brain. This
pathway plays a role in regulating stress responses and significantly impacting
a dog's
behaviour.
#6. Detoxification
Detoxification protects
dogs
against acute toxicity, whilst preventing accumulate of compounds to toxic
levels.
The microbiome impacts the way the body metabolises drugs. This
may explain why some dogs with the same disease respond
to certain treatments whilst others do not. In humans with cancer, the microbiome is
determining the response
to immunotherapies. The same likely applies to our dogs and pet dogs with cancer are
in clinical
trials investigating this.
#7. Competition
with Pathogens
A healthy, diverse microbiome may prevent
colonisation with harmful bacteria, by competing for nutrients and attachment sites along the gut
lining. This ‘competitive exclusion’ guards against gut infections and
overgrowth of harmful bacteria, causing dysbiosis.
Dysbiosis may increase production of certain toxins or
metabolites, affecting brain function and behaviour. Research shows [4] that overproduction of ammonia
and certain bacterial metabolites, contributes to cognitive decline and erratic
behaviours in dogs.
What can I do
to improve my dog’s microbiome?
To understand how we can improve our friend’s microbiome, we need
to understand the modifiable factors contributing to dysbiosis. The most common
culprits are antibiotics, dietary changes, and periods of illness or stress.
The primary way we can impact the gut microbiome is through
feeding a diet supporting good microbes and intestinal health, and adding
healthy microbes to the gut, via food.
✔️ A Balanced,
Diverse Diet
Dog food is a controversial, impassioned topic, but there are some
non-negotiables when it comes to the microbiome.
Feed a high-quality diet that meets the AAFCO's (Association of American
Feed Control Officials) standards and is appropriate for your dog's size, life
stage and health status. You can supplement this with various proteins and
vegetables, providing a plethora of beneficial nutrients, microbes, and
environmental enrichment for your pup!
Incorporate fresh, unprocessed foods that are safe for dogs. Bone broth, without seasonings and additives, is rich in gelatine and other nutrients, supporting the gut lining and is also anti-inflammatory.
I recommend pet parents research diet, visiting evidence-based sites.
If you plan
to make food at home, please work with a veterinarian and nutritionist to
ensure a balanced diet.
Vet
confession: I struggle to balance my own diet, let alone make a complete diet
at home for Hilda, so I supplement kibble with whole foods.
✔️ Consider
Probiotics and Prebiotics
- Probiotics are beneficial bacteria, added to the diet, which can temporarily help balance the microbiome.
Probiotic labels should include:
- the exact probiotic species (e.g., Bifidobacterium longum).
- the number of microorganisms (probiotics are measured in colony forming units, or CFU; 1-10 billion CFUs daily are recommended for dogs).
- an expiry date and storage conditions; and
- a guarantee for the number of live organisms.
- Prebiotics are non-digestible fibre that serves as food for the beneficial bacteria. [9] Prebiotics may include beet pulp, chicory root, gum arabica and high fibre vegetables.
(Synbiotics = a probiotic and prebiotic administered together).
✔️ Avoid
Unnecessary Antibiotics
Antibiotics save lives and are essential for treating certain
bacterial infections. However, they damage the microbiome, and must be used
judiciously, and only under
veterinary guidance. Inappropriate use also creates antibiotic resistance,
affecting our pets and us.
✔️ Regular
Worming
Routine worming protects against intestinal parasites (worms),
which may damage the gut lining, promoting dysbiosis. Parasites
can also be zoonotic, infecting humans.
✔️ Exercise
Regular exercise creates a more diverse and balanced gut microbiome for your pup
and for you! Grab that leash.
✔️ Minimise
Stress
Chronic stress alters
the microbiome, affecting digestion. Reduce stress in your dog’s environment
with a comfortable living space, and importantly, a consistent routine.
Positive training methods, socialisation, and environmental enrichment are also
critical.
✔️ Limit
Exposure to Toxins
Pesticides, herbicides, and cleaning agents negatively
affect the gut health [10]. Ensure your dog's environment is free from these harmful agents
where possible.
✔️ Regular Vet
Visits
Check in with your vet to detect any health issues early. At
minimum, an annual check-up is recommended.
✔️ Finally, avoid sudden changes in diet or introduction of supplements, and reach out to your vet when in doubt. Note any changes in your dog's stool, weight, thirst, appetite, energy levels and behaviour, as all of these may reflect changes in gut health and other diseases.
The canine microbiome has enormous influences on physical and mental health, and by appreciating this we can really help our friends. As the science progresses, more intervention and treatments will become available, so watch this space!
written by Dr Bec, August 2023 for Australian Dog Lover (all rights reserved).
About our writer
Dr Bec is a Melbourne-based veterinarian and academic, working in the clinic, animal welfare, the media and medical research. She has a passion for sharing fascinating facts and the latest research on the intriguing lives and science of all animals, particularly those we share our lives with.
Dr Bec is a regular guest on Melbourne radio, a columnist for Australian Dog Lover Magazine, Australian Cat Lover Magazine, and Pet Insurance Australia, and she presents short segments on all things animal related (see Insta and Facebook). Her emphasis is on sharing of evidence-based veterinary advances and the empowerment of pet parents, and society, through promoting medical literacy, or the understanding of our pets’ health, and our own. She relishes reaching out to all animal loving audiences.
Her academic and clinical research spans several areas, with a focus on the role of the microbiome in pet health, preventative medicine, developing new veterinary medicines, clinical trials that benefit animals and humans, and working to prevent antibiotic resistance.
Dr Bec advocates for animal charities that promote animal welfare, in Australia and overseas.
Her blog can be found at: www.drbecvet.com and she may be contacted at bec@drbecvet.com
References:
[1] Similarity of the dog and human gut microbiomes in gene content and response to diet - Microbiome. 2018; 6: 72. Published online 2018 Apr 19. doi: 10.1186/s40168-018-0450-3
[2] Gut instincts: microbiota as a key regulator of brain development, ageing and neurodegeneration - https://pubmed.ncbi.nlm.nih.gov/27641441/
[3] Gut Microbiota in Anxiety and Depression: Unveiling the Relationships and Management Options - Pharmaceuticals (Basel). 2023 Apr; 16(4): 565. Published online 2023 Apr 9. doi: 10.3390/ph16040565
[4] Dogs' Microbiome From Tip to Toe, Published online Epub 2021 Sep 10. - https://pubmed.ncbi.nlm.nih.gov/34509665/
[5] Characterization of microbial dysbiosis and metabolomic changes in dogs with acute diarrhea - PLoS One . 2015 May 22;10(5):e0127259. https://pubmed.ncbi.nlm.nih.gov/26000959/
[6] Factors Affecting Gut Microbiota of Puppies from Birth to Weaning - Published online 2023 Feb 6. doi: 10.3390/ani13040578[8] It's a Long Way to the Tap: Microbiome and DNA-Based Omics at the Core of Drinking Water Quality - Int J Environ Res Public Health. 2022 Jun 28;19(13):7940. https://pubmed.ncbi.nlm.nih.gov/35805598/
[9] Role of Gut Microbiota, Probiotics and Prebiotics in the Cardiovascular Diseases - Molecules. 2021 Feb; 26(4): 1172. Published online 2021 Feb 22. doi: 10.3390/molecules26041172
[10] Gut microbiota: a non-target victim of pesticide-induced toxicity - Gut Microbes. 2023; 15(1): 2187578. Published online 2023 Mar 15. doi: 10.1080/19490976.2023.2187578
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