Gastroenteritis is inflammation of the stomach and intestines, which is why you will often hear it called a tummy upset. It can affect any dog, from a mild bout that passes quickly to something serious, so the headline message is to speak to your vet rather than guess which kind you are dealing with.
At a glance
- What it is: inflammation of the stomach and intestines, usually causing vomiting and diarrhoea.
- Who it affects: dogs of any age or breed, though the PDSA says to contact a vet if your dog is very young or old.
- Urgency: contact your vet if your dog seems unwell, has blood in the vomit or stools, or cannot keep anything down. The PDSA says mild cases usually improve within one to two days.
- Vet needed? Often, yes. Speak to your vet if you are unsure.
Signs to look for
The PDSA lists these common signs:
- Diarrhoea, from loose stools to watery ones (see our guide to diarrhoea in dogs)
- Vomiting or retching (see vomiting in dogs)
- Eating less, or not at all
- Low energy (lethargy)
- A sore tummy: yelping when touched, or standing with the front legs down and back end up, the so-called praying position
- Blood or mucus in the stools
The PDSA adds that a lot of blood in the vomit or stools can point to a more serious form called haemorrhagic gastroenteritis (HGE).
Causes and risk factors
Gastroenteritis is a description of what is happening in the gut, not one single illness. According to the PDSA, causes include bacteria such as Campylobacter, viruses such as parvovirus, a sudden change of diet, parasites such as Giardia and other worms, swallowing toxins or objects that can cause a blockage, food allergies, inflammatory bowel disease and organ disease such as kidney or liver disease. Acute cases come on suddenly and usually pass within days or weeks, while chronic ones can last weeks to years and come and go.
For diarrhoea specifically, a 2025 Royal Veterinary College (RVC) VetCompass study in PLOS ONE looked at more than 2 million UK dogs. About 8.18% (roughly 1 in 12) needed vet care for acute diarrhoea in a year. Scavenging, underlying gastroenteritis, reactions to certain medicines and sudden diet changes were among the causes found, and dogs under 3 or over 9 years old were at higher risk than middle-aged dogs. Our piece on why dogs eat grass is a good reminder that dogs will put all sorts of things in their mouths.
When to call your vet
The PDSA says mild cases usually improve within one to two days, and a vet visit may not be needed if your dog seems well and is eating normally. Speak to your vet if your dog has:
- constant vomiting or very watery diarrhoea
- blood in the vomit or stools
- stopped eating or drinking, or just seems unwell
- no improvement within 24 hours
- an underlying illness, or is very young or old
The PDSA also says that if you are worried, contact your vet, even if the signs above do not match. Ring your own practice, or find one using our vets guide. Our sick dog symptoms guide can also help you judge how quickly to act, and a swollen belly with retching that brings up little or nothing needs an emergency vet straight away, as covered in GDV (bloat).
- 1. Notice
Vomiting, diarrhoea, eating less or low energy - 2. Speak to your vet
Speak to your vet if blood is present, or there is no improvement within 24 hours - 3. Vet examines
Questions about diet and timing; maybe blood tests, scans or a stool sample - 4. Options
Treatment options your vet may discuss: medicines, probiotics, fluid drip - 5. Ongoing care
Keep vaccinations and worming up to date; change diet gradually
How vets diagnose it
Per the PDSA, if your dog does not improve or gets worse, the vet may suggest blood tests, X-rays, ultrasound scans or a stool sample. Your vet will also ask what your dog has eaten and when the signs started, so it helps to have that ready.
What vets generally do about it
The PDSA describes several approaches, and which one suits your dog is your vet’s decision. They include medicine to settle vomiting, medicine to reduce stomach acid, probiotics, antibiotics only where they are actually needed, and hospital care with a fluid drip for dogs with serious signs or dehydration. The RVC authors of the diarrhoea study suggest that antibiotics are often not needed, and that owners who are concerned should seek veterinary advice. Treatment can be costly when overnight care is needed, so the PDSA suggests talking to your vet about options and costs, and taking out pet insurance early, before anything goes wrong.
Living with it and prevention
For a mild upset in an otherwise well dog, the PDSA has home-care advice on its page, but speak to your vet about what is right for your own dog first. The PDSA lists these ways to lower the risk:
- keep vaccinations and worming up to date
- stop scavenging by keeping dogs away from bins and food waste, and teaching a drop command
- change diet gradually, mixing old and new food over about two weeks
The RVC’s lead author put it neatly: a consistent diet leads to consistent poo.
Related conditions
You can browse the full list in our dog illnesses and conditions A to Z.
Sources
- PDSA, Gastroenteritis (stomach upset) in dogs
- Royal Veterinary College VetCompass, New RVC study gets to the bottom of what causes doggy diarrhoea (summarising O’Neill et al., Epidemiology and clinical management of acute diarrhoea in dogs under primary veterinary care in the UK, PLOS ONE, 2025)
Frequently Asked Questions
What is gastroenteritis in dogs?
It is inflammation of the stomach and intestines, usually causing vomiting and diarrhoea. It ranges from mild to severe, so speak to your vet if you are unsure.
How long does gastroenteritis last in dogs?
The PDSA says mild cases usually improve within one to two days, and acute cases usually settle within days or weeks. If there is no improvement within 24 hours, speak to your vet.
Does my dog need antibiotics for gastroenteritis?
Not always. The PDSA says many cases are not bacterial, so antibiotics are only sometimes used. That decision belongs to your vet.
Is blood in my dog’s poo or vomit an emergency?
The PDSA lists blood in the vomit or stools as a reason to contact your vet, and a lot of blood can point to a more serious form called HGE. Contact your vet promptly.
This page is general information, not veterinary advice. If you are worried about your dog, speak to your vet. Written by Georgiana & Figo, who are dog owners, not vets. Have a look around Calmshops for everyday dog essentials.
