Bloated stomach in cats: causes, diagnosis and complete treatment

Is your cat's stomach swollen and you're not sure if it's just a passing thing or a serious problem? Seeing a feline with a larger-than-normal belly usually sets off alarm bells, and rightly so. A distended abdomen can be due to simple digestive issues or complex illnesses that require immediate veterinary attention.

When we notice that our pet's abdomen is more swollen, hard, or soft than usual, it's crucial to determine the cause as soon as possible to provide the appropriate treatment. A swollen stomach or belly in cats isn't a disease in itself, but rather a symptom that something is wrong in the body , ranging from simple indigestion to serious conditions such as feline infectious peritonitis (FIP), liver problems, cancer, or fluid accumulation (ascites).

In this special feature, we'll review, in detail and from a practical perspective, all the most common causes of abdominal swelling in cats , how they manifest, how they are diagnosed, and what treatment options are available. We'll also discuss when you should take your cat to the vet immediately and what you can do at home to improve your feline's well-being while you wait for the appointment.

When should we worry

Not all swollen bellies in cats indicate a serious illness . Some cats, after eating very anxiously or consuming more food than usual, may experience mild, temporary abdominal distension. In these cases, the animal may seem somewhat uncomfortable, but if it behaves normally and the bloating subsides within a few hours or a couple of days, it is usually just a case of mild indigestion or gas.

However, there are clear warning signs that indicate we should go to the vet without delay:

The cat is eating normally or even has lost its appetite, and suddenly a larger than usual belly appears.
My belly is very tense and hard to the touch, or on the contrary, very soft and with a liquid sensation inside.
They look themselves breathing difficultiespanting, open-mouth breathing, or a posture with the neck stretched out to try to breathe better.
Hay intense apathyThe cat hides, stops interacting, or doesn't respond as usual.
Appear recurrent vomitingdiarrhea, or the cat stops urinating and/or defecating.
is detected rapid weight loss despite the swollen belly.

When a cat's abdomen suddenly swells without any apparent cause related to food, it can be the first indication of a serious illness: feline infectious peritonitis , cancer , hepatitis , liver necrosis , heart problems, ascites, internal trauma, or even pyometra in the case of intact female cats.

It's also important to differentiate between a swollen abdomen due to fat accumulation (obesity) and an abdomen that increases in size quickly. Obesity causes a more sagging and softer belly, but this changes slowly , while sudden swelling is usually associated with fluid retention (ascites) , severe inflammation, or internal masses.

Feline infectious peritonitis (FIP) and other peritonitis

Feline infectious peritonitis (FIP) is one of the most common causes of a swollen, soft abdomen due to fluid accumulation . It is an infectious disease that occurs when a cat's body reacts abnormally to feline coronavirus (FCoV) infection . Many cats can come into contact with this virus and clear it without problems, but in some cases, the virus mutates and triggers FIP.

This is an inflammation of the blood vessels (vasculitis) that causes fluid and protein to leak into cavities such as the abdomen and, sometimes, the chest. Without proper treatment and close monitoring, it can be fatal.

In the so-called effusive or wet form of FIP, this inflammatory fluid accumulates in the abdominal cavity, resulting in a cat with a swollen, soft, and progressively enlarging abdomen . In addition, the following often appear:

persistent fever that does not respond well to usual treatments.
Weight loss despite the large abdomen.
Marked lethargy and lack of interest in the environment.
In some cases, respiratory distress if fluid also accumulates in the chest.

Diagnosing FIP is complex. The veterinarian can rely on:

Abdominal ultrasound to check for the presence of fluid and the condition of internal organs.
Abdominal fluid analysis (abdominocentesis) to assess its appearance (it is usually yellowish, viscous) and its composition.
Blood Tests with typical alterations, such as hyperglobulinemia.
In some cases, biopsies or specific tests for feline coronavirus.

Not all peritonitis is infectious. There is also pyoperitoneum , which is an accumulation of pus in the abdominal cavity secondary to severe infections, intestinal perforations, or organ ruptures. In these cases, the fluid is cloudy and purulent , and the cat usually presents with high fever, intense pain, hunched posture, and a very tender abdomen . This is an absolute emergency.

The therapeutic approach to any peritonitis combines, depending on the case, hospitalization, fluid therapy, drainage of abdominal fluid, antibiotics, anti-inflammatories and, often, surgery to solve the underlying cause (perforation, foreign body, infected uterus, etc.).

Abdominal cancer and tumors

Cancer can also cause a cat to have a swollen stomach or belly. In felines, any change in their routine or in the way they move, groom themselves, or interact with us can be a sign that something is wrong.

Abdominal tumors can cause swelling in two main ways:

Due to the growth of the tumor mass itself, which occupies space in the abdomen and displaces organs.
Due to the appearance of ascitesThat is, accumulation of free fluid in the abdomen as a result of compression of blood vessels or organs (liver, lymphatics, etc.).

The most common symptoms of cancer in cats that affect the abdomen include:

Chronic diarrhea or intermittent.
Loss of appetite and weight progressive.
Recurring vomiting, sometimes with blood or bile.
Depression, apathy and less interaction with family.
Isolation and changes in behavior.
Sometimes respiratory distress if there is also fluid in the chest.

The problem is that these signs can be confused with other digestive or liver conditions, so by the time cancer is detected in cats, the tumor has often already spread . Therefore, whenever you notice any change, no matter how small it may seem, it's advisable to consult your veterinarian.

The diagnosis usually requires:

Abdominal ultrasound to locate masses and assess their size.
X-rays to see organ displacement or metastasis.
Blood Tests to assess the animal's overall condition.
Puncture or biopsy of the mass or abdominal fluid to confirm the type of tumor.

Treatment depends on the type and extent of cancer: it may include surgery, chemotherapy, palliative treatments, and in some cases, drainage of abdominal fluid to relieve pressure and improve breathing.

Hepatitis and other liver diseases

Hepatitis occurs when the liver becomes inflamed and unable to eliminate toxins normally. This inflammation can be caused by diabetes, feline leukemia, infections, poisoning, or chronic inflammatory diseases . When a cat suffers from progressive liver disease, it is common to see:

Increased thirst (drinks more water than usual).
Increased frequency of urination.
Duller hair, dull and with a neglected appearance.
Swollen abdomen due to fat accumulation around the liver or ascites.
In advanced stages, jaundice (yellowish mucous membranes) and marked weakness.

Sometimes liver tumors or conditions like cirrhosis appear , which, by reducing the liver's ability to produce proteins (especially albumin), promote fluid accumulation in the abdomen . In these cases, the abdomen is swollen, but the rest of the body may appear thin and with muscle loss.

Treatment will depend on the underlying cause. In very ill cats, hospitalization is often necessary for several days to receive intravenous fluids, medication, and nutritional support. Once home, a specific diet for liver disease, low in sodium and with high-quality protein , is usually recommended to reduce the burden on the liver and minimize the risk of further episodes.

Hepatic necrosis and liver failure

The word "necrosis" means tissue death, and "hepatic" refers to the liver. Therefore, hepatic necrosis implies that part or all of the liver undergoes irreversible changes that prevent it from performing its functions . When necrosis affects only a portion of the liver, it may go unnoticed, but if it spreads, it can lead to severe liver failure.

The liver is the organ responsible for detoxifying the body, producing essential proteins, and regulating fluid balance . When this organ fails, the body cannot maintain internal equilibrium, and multiple symptoms appear:

frequent vomiting, with or without blood.
Marked weight loss and reduced appetite.
High blood pressure and possible neurological alterations in advanced cases.
Ascitis (accumulation of fluid in the abdomen), which causes a large belly and a feeling of heaviness.

To detect this type of liver problem, the veterinarian usually performs the following tests:

Abdominal ultrasound to check the appearance of the liver and the presence of fluid.
Complete blood tests to assess liver enzymes, plasma proteins, coagulation and other parameters.
In some cases, liver biopsy to determine the type of injury and its prognosis.

The treatment, again, depends on the cause. It can result from severe hepatitis, an infection, a tumor, or poisoning. Depending on the diagnosis, the doctor will prescribe specific medication, a tailored diet, and rest . In extreme situations, and when medically feasible, a liver transplant may be considered , although it is not an option available in all centers or countries.

Ascites in cats: a swollen belly due to fluid

When we talk about ascites (also called hydroabdomen), we are referring to the abnormal accumulation of free fluid in the abdominal cavity . It is not a disease in itself, but a sign of a serious imbalance in the body . This fluid can have very different compositions, depending on the cause.

Pure transudateClear, low-density fluid, typical of liver or heart problems that reduce oncotic pressure or cause venous congestion.
Modified transudate: with slightly more protein, common in cases of chronic inflammation, cirrhosis or certain neoplasms.
Exudate: cloudy fluid, rich in proteins and inflammatory cells, which usually indicates infections or peritonitis, such as the wet form of FIP.
Kilo: milky fluid rich in fat (chyloperitoneum), associated with lymphatic problems or rupture of lymphatic vessels.
BloodHemoperitoneum, which appears after trauma, ruptured tumors, or vascular injuries.

The diseases that most frequently cause ascites in cats include:

Liver diseases (cirrhosis, liver failure, chronic hepatitis, liver neoplasms) that decrease albumin synthesis and alter the portal circulation.
Heart diseases, especially right heart failurewhich raise venous pressure and promote the leakage of fluid into the abdomen.
Feline infectious peritonitis (wet form), with yellowish and sticky exudate.
Hypoproteinemia and hypoalbuminemia, due to protein loss through the kidney (nephropathies) or the intestine (protein-losing enteropathies).
Lymphatic problems, such as lymphangiectasia or lymphatic tumors that obstruct lymph drainage.

The main symptoms that usually accompany ascites, in addition to a swollen abdomen, are:

Respiratory distress by pressure on the diaphragm.
Lethargy and weakness, rejection of play and exercise.
Loss of appetite and progressive weight loss.
In some cases, vomiting or diarrhea if the cause is digestive.
Exercise intoleranceespecially in cases of heart failure.

The diagnosis is based on a combination of:

Physical examination and palpation of the abdomen to detect liquid fluctuation.
Abdominal ultrasoundwhich is the most effective test to confirm the presence of fluid and assess the organs.
Abdominal and chest x-rays, useful for seeing masses, cardiomegaly or displacements of structures.
Abdominocentesis (extraction of a liquid sample) to classify and analyze it in the laboratory.
Blood Tests to evaluate liver, kidney, plasma proteins, inflammation, and infections.
In cases of suspected heart disease, echocardiography to study the function of the heart.

Treatment focuses on relieving symptoms and treating the underlying disease :

Abdominal fluid drainage (abdominocentesis) in severe cases to improve breathing. It is a palliative procedure that does not address the underlying cause.
specific diet for liver, heart or intestinal disease, reducing sodium and strengthening protein quality.
Diuretic drugs and cardiac or hepatic medications depending on the cause.
Stress management and rest to reduce general discomfort.

Other possible causes of a bloated stomach

In addition to the serious illnesses already mentioned, there are other relatively common causes of a swollen stomach or abdomen in cats that we should be aware of. Some are milder, but still require monitoring, while others can become quite serious if not treated promptly.

Intestinal parasites

Internal parasites are especially common in newly adopted kittens, stray cats, or cats that go outdoors without regular deworming . Nematodes, tapeworms, and protozoa (such as Toxoplasma gondii or Giardia ) can cause:

Protruding belly, often soft, typical of kittens with worms.
intermittent diarrhea or pasty, sometimes with mucus or blood.
Weight loss or poor development despite a good appetite.
Dull hair and a neglected appearance.

In some animals, the symptoms are minimal, perhaps just mild diarrhea. Even so, it's crucial to deworm your cat as soon as possible and follow a regular internal deworming schedule, which in most cases is recommended every three months , adjusting the schedule to the animal's lifestyle. In addition, vaccinating your cat when it's healthy and of the appropriate age is an important complementary measure to prevent disease and should be planned according to the schedule recommended by your veterinarian.

Internal parasites are not usually transmitted to humans if basic hygiene practices are followed : using gloves or a scoop to clean the litter box, washing hands before eating, preventing children from handling feces, and keeping deworming up to date. When cats go outdoors or hunt, the chances of infestation increase, so prevention is essential.

Indigestion and overeating

Indigestion occurs when a cat eats more than it should or ingests something unsuitable. The stomach becomes distended , and the animal feels unwell. Common symptoms include:

Swollen and somewhat painful stomach upon touching it.
Occasional vomiting shortly after eating.
Increased body temperature, and may lead to fever if it exceeds 39,5 ºC.
Slight apathy and a preference for resting.

In most healthy cats, these episodes resolve within a few hours or a couple of days at most, provided their appetite and activity level improve. It's advisable to monitor the amount of food, divide meals into smaller portions, and avoid sudden changes in diet . Blood pressure may also temporarily increase in some cases due to stress and associated inflammation.

However, if you notice that your cat is having trouble breathing , is not urinating or defecating , or is in very intense pain, you should seek veterinary attention immediately , as it could be an intestinal obstruction or another more serious problem and not just indigestion.

Poisoning

Another likely cause of a swollen stomach or belly is poisoning , whether from ingesting a plant treated with chemical insecticide , poisoned bait , human medicines , or cleaning products.

In these cases, in addition to abdominal bloating, the following may appear:

Intense vomiting, often with traces of the toxic substance.
Diarrhea, sometimes bloody.
Tremors, seizures, or incoordination.
Excessive salivation and chemical bad breath.
Respiratory problems and extreme weakness.

If you suspect your cat has been poisoned, you should take it to a veterinary clinic as soon as possible , ideally bringing a sample of the product or the original container so that the professional can identify the toxin and act more quickly and accurately.

Inflammatory bowel disease, gastritis, and other chronic digestive problems

Some cats experience chronic digestive problems that, over time, can lead to general weight loss and, in some cases, a distended abdomen due to inflammation, gas, or alterations in intestinal motility.

Inflammatory bowel disease (IBD) is one of the most common causes of prolonged digestive disorders in cats. It is characterized by persistent inflammation of the intestinal lining , which interferes with the proper absorption of nutrients. It can affect the small intestine, the large intestine, or even the stomach.

The most common signs include:

Recurring vomiting without a clear cause.
Chronic diarrhea or alternating soft and normal stools.
progressive weight loss despite a relatively preserved appetite.
Decreased appetite in more advanced stages.
Lethargy and less interaction with the environment.
Rough or unkempt hair.

Diagnosis requires ruling out other causes (parasites, food allergies, pancreatic insufficiency, lymphoma, etc.) through stool analysis, blood tests, ultrasounds, and even intestinal biopsies . Treatment usually combines a hypoallergenic or hydrolyzed diet, corticosteroids, probiotics, and, in some cases, specific antibiotics.

Gastritis , on the other hand, is inflammation of the stomach. It can be acute (due to eating something unsuitable, ingesting foreign objects, or taking certain medications) or chronic. Its symptoms include :

frequent vomiting, with or without blood.
Abdominal pain and evasive behavior.
Loss of appetite.
In severe cases, gastric ulcers and anemia.

Acute gastritis in otherwise healthy cats can be treated with controlled fasting, gradual reintroduction of food, and a bland or specific diet . If the cat has other illnesses or the gastritis becomes chronic, a thorough examination is essential to identify the cause and reduce the risk of complications.

Abdominal trauma and pyometra

Abdominal trauma is another potential cause of a swollen, soft, or tense abdomen . This can be due to being hit by a car, falling from a great height, kicking, or other severe blows . In these cases, the swelling may be caused by:

Rupture of the spleen, liver, or kidneyswith internal bleeding and blood accumulation in the abdomen.
Bladder rupture, with leakage of urine into the abdominal cavity.
Intestinal lesions that cause peritonitis and cloudy fluid with blood.

These are extremely serious situations requiring immediate veterinary assistance . The veterinarian will stabilize the cat, perform X-rays, ultrasounds, and blood tests , and decide if urgent surgery is necessary . Prevention involves keeping the cat in a safe environment, monitoring windows and balconies, and preventing it from going outside unsupervised.

In unspayed cats, pyometra (a serious uterine infection) can also cause abdominal distension , intense discomfort, and, in its closed form, an accumulation of pus within the uterus. If the uterus ruptures, its contents leak into the abdomen, causing severe peritonitis with a very painful and swollen belly.

Signs of pyometra include:

Fever and apathy.
Loss of appetite and increased thirst.
Purulent vaginal discharge in the open form.
Distended abdomen and painful in advanced forms.

The treatment of choice is surgery to remove the uterus and ovaries (ovariohysterectomy) and strong medical support. The best prevention is early spaying of cats, which also prevents other reproductive and hormonal problems.

If you notice any changes in the size, consistency, or tenderness of your cat's abdomen, especially if accompanied by lethargy, difficulty breathing, vomiting, diarrhea, fever, or weight loss , it's best to take them to the vet as soon as possible for an early diagnosis. Identifying the cause early is the best way to ensure effective treatment and a faster, more complete recovery for your feline companion.