What this means
Fat builds up slowly and evenly: a plump cat gets rounder all over and its ribs are hard to feel. It is different when only the belly swells while the spine, ribs and hip bones grow more prominent. That can mean fluid is collecting in the belly or an organ is growing while the muscles waste away. Some cats have a loose flap of skin on the lower belly that swings as they walk: that is normal and does not make the belly swell.
In a kitten, a swollen, drum-like belly can mean intestinal worms. In a young cat that also has a fever, stops eating and loses weight, such a belly can be a sign of infectious peritonitis. An unspayed female may be pregnant.
Notice whether the belly is soft or hard, whether your cat lets you touch it, whether it eats, passes stools and urinates as usual, and whether it breathes easily. Do not press or massage the belly: a vet has to find the cause.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your cat.
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Feline infectious peritonitis
In the wet form of this disease a thick, yellowish fluid collects in the belly. The cat also has a fever, stops eating and loses weight.
About the condition: Feline infectious peritonitis (FIP) -
Intestinal worms in a kitten
A heavy load of worms bloats a kitten's belly, and it grows poorly and may have diarrhoea or vomit.
About the condition: Intestinal worms -
Fluid build-up from another illness
Fluid can collect in the belly with heart, liver or kidney disease, or when the blood is short of protein. The cat may also lose weight and be listless.
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Excess weight
Fat collects on the belly and all over the body, and the ribs are hard to feel. The belly is then soft and the cat behaves as usual.
About the condition: Obesity (excess weight) -
An overfull bladder or held-back stools
When the urethra is blocked or the cat has not passed stools for a long time, the belly becomes tight and painful. The cat squats and strains in the litter box, which can be an emergency.
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An enlarged organ or a growth in the belly
An enlarged liver, spleen or kidneys, or a tumour, can swell the belly. Only a vet can tell, with tests.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the belly is soft, or hard and tight
- Whether the belly is growing, and how fast
- Whether your cat is getting thinner elsewhere, with the spine and ribs showing more
- Whether it eats, passes stools and urinates as usual
- Whether it has a fever or has turned listless
- Whether a kitten's stools contain worms
When to book a routine visit
Book an examination if your cat's belly is growing while the rest of it is not, or a kitten's belly has swollen. If your cat is also off its food, feverish or losing weight, contact a vet the same day.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Feline infectious peritonitis (FIP) Infections A severe disease that develops when the coronavirus living in cats' guts changes inside a cat's body and starts spreading throughout it. It inflames blood vessels and organs, and fluid can collect in the belly or chest.
- Intestinal worms Parasites Parasites that live in a cat's gut: roundworms, tapeworms and others. They take nutrients, irritate the gut and can slow a kitten's growth.
Body systems: Infections Parasites