Why Does My Dog Have a Swollen Belly?

Bloat and GDV

GDV (gastric dilatation volvulus) is when the stomach fills with gas and then twists, blocking both the entrance and exit. A twisted, gassy stomach can squash blood vessels and press on the lungs, making it hard to breathe. Bacteria can also leak into the blood, and the spleen can twist too.

Blue Cross says bloat can kill in a matter of hours without veterinary treatment, while Vets Now says it can kill within minutes. Blue Cross also notes that bloat is rare.

Pyometra (infected womb)

Pyometra is a womb infection in unneutered females, and PDSA calls it an emergency. Symptoms include pus from the vulva, drinking more, vomiting, a bloated abdomen, lethargy, not eating and collapse. It is most common four to eight weeks after a season, and the risk is higher over six years old. Neutering prevents it.

In a closed pyometra there may be no discharge, which makes it less obvious and more dangerous. Blue Cross says it needs urgent veterinary attention, and the usual cure is emergency surgery.

A blocked bladder

A blocked bladder can come with a swollen or painful tummy. PDSA says being unable to pass urine is life threatening, so call the vet immediately. VCA adds that a blocked urethra can make the bladder swell and possibly rupture.

Fluid in the abdomen

VCA says free fluid in the abdomen is always a cause for concern. It can be urine, blood or an effusion. Effusions can develop from liver disease, heart disease, abdominal tumours, low blood proteins and inflammation of the abdominal lining, and VCA says they should always be investigated.

Right-sided heart failure can make the abdomen fill with fluid, a condition called ascites. VCA lists a swollen belly among signs of heart failure, along with coughing, tiring easily, excessive panting and pale or bluish gums. PDSA also lists a painful or bloated belly among signs of more serious liver disease.

Internal bleeding

Free blood in the abdomen is linked to trauma, surgery, bleeding disorders and some tumours. VCA says a dog hit by a car with sudden swelling is more likely to be bleeding internally.

Cushing's disease and hormonal causes

PDSA lists a "pot-belly" among Cushing's disease signs, alongside excessive drinking and peeing, bald patches, hunger, thin skin and low energy. Blue Cross says it can cause swelling that makes the belly appear to sag. There is no simple single test, so diagnosis can take time.

VCA explains that Cushing's can enlarge the belly through liver enlargement, abdominal fat and a weakened body wall, and that hypothyroidism can also cause a bulging belly. Learn more in What is Cushing's Disease?

Worms in puppies

PDSA lists a pot-belly and bloating, most common in puppies, as a roundworm symptom. Others include weight loss, diarrhoea, vomiting and poor growth. Roundworm rarely causes serious illness in adult dogs but can make puppies very ill, and many puppies catch it in the womb or from mum's milk.

As a general rule, PDSA says puppies are wormed from about three weeks old and then every two to three weeks until they are 16 weeks old. Adult dogs are usually wormed every one to three months. Each product has its own guidelines, so check with your vet which wormer suits your dog's age and weight.

PDSA also says prescription wormers, which are supplied by a vet or by an online pharmacy against a prescription from your vet, are far more reliable than non-prescription products.

Weight gain, pregnancy and growths

Fat can build up in the abdomen and enlarge the belly. Weight gain is usually from eating too much, too little exercise, or both. PDSA suggests checking your dog's shape: you should see a waist from the side and above, and the tummy should go in, not bulge out.

Pregnant dogs show belly enlargement by mid to late pregnancy. Organ enlargement and tumours, whether cancerous or not, can also swell the belly.