There are many different causes for abdominal swelling in dogs, ranging from milder cases that are unrelated to digestion to emergency situations (such as with bloat). The most common ones are:
The abdomen of a dog with many intestinal worms can appear distended and round. Typically it will still remain fairly soft, and the dog is not in pain. This occurs most commonly in puppies who have not been given deworming medication, but is possible in older dogs if they have become infected with intestinal worms and have not received regular deworming medication.
Some types of worms are visible in a dog’s feces, or can be seen as small white pieces of worm that look like grains of rice around your dog’s anus (such as with tapeworms). Several other intestinal worms remain within the intestine and your dog will pass microscopic eggs within their stool. Your veterinary team will talk to you about deworming medications and stool sampling at your dog’s annual physical exam.
If your dog is constipated, they may have a mildly firm and swollen abdomen. It’s normal for your dog to pass stool at least once a day. Signs that they’re constipated can include repeated straining to defecate and signaling the need to go outside with no success in passing stool once they’re out.
They also may be passing only small firm pieces with much effort. Urinary blockages are a more urgent emergency, so if you have any doubt whether your dog is passing urine, you should contact your veterinary clinic immediately.
For intact female dogs who are in the presence of intact males, don’t forget to keep pregnancy on your list of possible causes of an enlarged abdomen. The length of gestation (pregnancy) in a dog is about two months, so by the time you notice an enlarged abdomen several weeks will have passed since your dog was in contact with the male. Your veterinarian will be able to feel your dog’s abdomen to determine whether they are likely pregnant, and then will perform x-rays to confirm if this is the case.
If your dog is in heart failure, their abdomen may appear swollen with fluid backing up from the heart. This symptom is evident in advanced heart disease, typically in cases where it has gone undiagnosed and the dog is therefore not currently receiving treatment. Dogs with heart disease will also commonly exhibit exercise intolerance.
A serious cause of abdominal swelling that requires immediate veterinary assistance is stomach bloat. In these emergency situations, your dog’s stomach can become very distended with food or gas. This is extremely painful for the affected dog. Bloat can progress into a much more serious condition called gastric dilatation and volvulus (GDV), which is where the stomach twists, cutting off circulation and preventing the stomach contents from moving into the intestines.
This condition is more common in large, deep chested dogs such as Great Danes, Irish Wolfhounds, and Standard Poodles. The risk increases if they are only fed once a day, and are therefore ingesting a large amount of food at once. It is advisable to split meals into twice a day feeding, and to avoid any rigorous exercise after eating. This condition can be fatal, so if you notice your dog appearing bloated and painful, contact your veterinary clinic immediately.
Pro Tip: Feed your dog two meals a day instead of one, and always avoid any rigorous exercise after eating to help prevent bloat.
A tumor within the abdomen can cause a swollen appearance, as it takes up room within a dog’s belly. Tumors can originate from different organs, and vary in how serious they are and whether they have the potential to spread to other parts of the body.
Tumors of the spleen are one of the more serious types of tumors that can present as an emergency, as they have the potential to rupture, causing a dog’s abdomen to fill with blood. If a ruptured splenic tumor is caught early, your dog’s abdomen will appear swollen and they will be very painful, likely panting and pacing. In more serious cases, the dog may collapse to the floor suddenly if the ruptured tumor causes a large amount of blood loss into the abdomen.
Cushing’s Disease, also known as hyperadrenocorticism, can cause a dog to have the appearance of an enlarged abdomen. Dogs who have this condition are producing extra steroid hormones from their adrenal glands, resulting in the dog’s pot-bellied appearance. If your veterinarian is suspicious of this condition, they will speak to you about blood and urine screening tests, and will likely recommend an abdominal ultrasound.
Uterine Infection (Pyometra)
Intact female dogs (those who are not spayed) have an increasing risk of uterine infection as they age. This infection causes the uterus to fill with pus, and it can become very distended within the abdomen, causing the whole abdomen to appear larger.
Typically the first sign will be pus draining from your dog’s vulva, which may be clearly visible, or you may notice her continually licking at her back end. Your veterinarian can diagnose this condition by x-rays and it is almost always treated by surgery to spay the dog and remove the uterus. Depending on how advanced the infection is, this may be an emergency surgery.