Stress diarrhoea in dogs: how the mind affects digestion

Moving house, boarding, a car journey, visitors, fireworks. Stress can show up in a dog’s stool, even when the food has not changed at all. It is no coincidence: the brain and the gut are constantly communicating. Scientists call this the gut-brain axis.

Why does stress change digestion?

Stress changes a dog’s digestion because the brain and the gut send each other signals through nerves and hormones, in both directions. This link is called the gut-brain axis, and it is best described in humans. We have less data for dogs, so it matters to separate what is established from what is not.

• The mind affects the gut. According to VCA, stress colitis is one of the main causes of large bowel diarrhoea in dogs.
• The gut is linked to the mind. In two smaller studies (31 and 42 dogs), dogs with fears or aggression had a different gut bacteria make-up from dogs without these problems (Kirchoff et al., 2019; Mondo et al., 2020). This is an association, not proof of cause.
• Data from humans. The link between brain and gut is best described in review papers on humans (Mayer et al., 2006). In dogs, such detailed data do not exist yet, so here we only say that an association exists.

How can you tell a dog is stressed?

You can tell a dog is stressed from its body language and changes in behaviour, often before its tummy complains. According to the AKC, a dog may lick its lips, yawn, pant without exertion, turn its head away, tuck its tail or show the whites of its eyes. A single sign on its own does not have to mean anything. The AKC advises always judging behaviour in the context of the individual dog and the situation.

An Italian study with 1,190 owners showed that people most often recognise trembling and whining, and sometimes aggression, excessive barking and panting (Mariti et al., 2012). Few owners reported subtle signals such as turning the head away, yawning or licking the nose. So pay more attention to the small things: a dog that yawns and licks its lips when visitors are over may be telling you it has had enough.

Which situations stress a dog, and what can help?

A dog is often thrown by a change of environment, noise and separation from its person. The table sums up common situations and general steps that may help a dog cope.

How can you recognise stress diarrhoea?

Stress diarrhoea is loose stool that appears during a demanding period or shortly after it. Typically it is frequent small amounts of loose stool, sometimes with mucus or a little blood. Your dog may strain or urgently want to go outside. According to VCA, most dogs with stress colitis return to normal within three to five days. But do not wait that long at home: if the diarrhoea lasts longer than one to two days or there is even a little blood in it, call your vet, so they can judge whether it really is stress.

How do you prepare your dog for boarding or a journey?

The best way to prepare your dog for boarding or a journey is to let it get used to it gradually and not to change anything else. The more things stay familiar, the less strain on your dog and its tummy. The AKC recommends planning ahead for predictable stressors such as fireworks or car travel.

1. Get your dog used to it gradually. Start with a short separation or a short drive and lengthen it slowly. Try boarding first for a few hours.
2. Take its own food. A dog at a boarding place gets what it is used to, in the same portion and at the same times. Save any novelties for another time.
3. Do not introduce anything new. No new treats, chews or supplements just before a stressful situation. If you do need to change the food, do it gradually and in a calm period.
4. Pack familiar things. A blanket, a toy or clothing with your scent will help your dog feel more secure.
5. Keep the routine. Regular feeding, walks and sleep give your dog a sense of security. Offer it a quiet hideaway where it can retreat.
6. Handle fireworks in advance. The British charity PDSA advises walking your dog in daylight during the season, drawing the curtains before dusk and playing music. According to PDSA, sound training takes several months, so start it long before the season, ideally after consulting a vet or a behaviourist.

Why is it good to start early?

• 1/4 to 1/2of dogs show signs of fear of noise, according to a British study (a quarter in the questionnaire, almost half in the detailed interviews).survey of 3,897 owners and interviews with 383 owners · Blackwell et al., 2013
• under 1/3of the owners of such dogs sought professional help.Blackwell et al., 2013

Fear of noise can be managed, but it takes time. The sooner you start, the calmer your dog and its tummy will be.

When is something else behind repeated “stress” diarrhoea?

Repeated diarrhoea that also appears outside demanding periods may have a cause other than stress. Stress is only one of the reasons. If the problems keep coming back or last longer, medical causes need to be ruled out first.

• Intestinal parasites. According to the Merck Veterinary Manual, when colitis is suspected, the work-up includes a stool test for parasites, for example for whipworm (Trichuris vulpis) and giardia. Whipworm sheds its eggs intermittently, so one negative result does not rule out infection. According to VCA, parasites, such as giardia and whipworm, are among the possible causes of colitis.
• Chronic enteropathy. This is a long-term gut disease that shows up in dogs as repeated problems, such as diarrhoea or vomiting (Dandrieux, 2016). The approach is chosen by the vet and often starts with a change of diet and further tests.
• Another cause. It could be, for example, a food intolerance or something your dog ate.

You will find a more detailed breakdown in the article Soft stool in dogs: causes and what to do, and the appearance of stool is described in Dog poop: what colour, shape and consistency reveal. If diarrhoea appears after a change of food, the article Switching dog food: a 7 to 10 day plan will help. A general procedure for diarrhoea is summarised in the article Diarrhoea in dogs: what to do and when to see a vet.

Every dog reacts differently

Every dog has a different make-up of gut bacteria and reacts to strain in its own way. If your dog’s digestion is repeatedly upset in demanding periods, it makes sense to discuss it with your vet and to know the baseline. You will find more on what a microbiome analysis can do in the article Dog microbiome test: what a stool analysis can show.

Sources

1. Kirchoff NS, Udell MAR, Sharpton TJ (2019). The gut microbiome correlates with conspecific aggression in a small population of rescued dogs (Canis familiaris). PeerJ. doi.org/10.7717/peerj.6103
2. Mondo E et al. (2020). Gut microbiome structure and adrenocortical activity in dogs with aggressive and phobic behavioral disorders. Heliyon. doi.org/10.1016/j.heliyon.2020.e03311
3. VCA Animal Hospitals. Colitis in Dogs. vcahospitals.com/know-your-pet/colitis-in-dogs
4. Blackwell EJ, Bradshaw JWS, Casey RA (2013). Fear responses to noises in domestic dogs: Prevalence, risk factors and co-occurrence with other fear related behaviour. Applied Animal Behaviour Science. doi.org/10.1016/j.applanim.2012.12.004
5. PDSA. Dogs and fireworks. pdsa.org.uk
6. Patel KV, Hunt ABG, Castillo-Fernandez J et al. (2024). Impact of acute stress on the canine gut microbiota. Scientific Reports. doi.org/10.1038/s41598-024-66652-3
7. Mariti C et al. (2012). Perception of dogs’ stress by their owners. Journal of Veterinary Behavior. doi.org/10.1016/j.jveb.2011.09.004
8. Mayer EA et al. (2006). Review article: modulation of the brain-gut axis as a therapeutic approach in gastrointestinal disease (data from humans). Alimentary Pharmacology & Therapeutics. doi.org/10.1111/j.1365-2036.2006.03078.x
9. American Kennel Club. Signs of Stress in Dogs: What to Watch For. akc.org
10. Merck Veterinary Manual. Colitis in Small Animals. merckvetmanual.com
11. Dandrieux JRS (2016). Inflammatory bowel disease versus chronic enteropathy in dogs: are they one and the same? Journal of Small Animal Practice. doi.org/10.1111/jsap.12588