Sudden Weight Gain in Dogs: Why Has My Dog Expanded in Front of My Eyes?

I believe that every time you use the word sudden when describing your dog’s symptoms, you should figure that the urgency of treatment is equal to the speed of onset. Sudden is a synonym for acute.

Obesity is a real epidemic, but no dog goes to bed skinny and wakes up fat.

When it appears that they do, something is seriously amiss.

Some conditions can cause your dog to gain weight or look like they did relatively quickly, such as underactive thyroid or Cushing’s disease. But that doesn’t happen overnight either. So none of these things should be ignored, but they don’t constitute an emergency.

Acute onset

If it happens acutely, you’re not looking at weight gain but distention or swelling.

In large breed dogs, a common cause of a sudden expansion of the abdomen–and a mother of all emergencies–is GDV, gastric dilatation-volvulus, also referred to as bloat. While there is a difference between bloat and GDV, the former can quickly turn into the latter. The abdomen will be visibly enlarged. Your dog might be retching without anything coming out, having difficulty breathing, and acting distressed. GDV is extremely painful and can quickly become deadly.

If your dog has symptoms like these, call your veterinarian immediately.

Enlarged appearance

Blood or fluid accumulation in the abdomen will also make the belly look enlarged.

A splenic tumor, for example, whether benign or cancerous, can rupture and bleed into the abdomen. Your dog may also act lethargic, weak, and have pale mucous membranes. This, too, is an emergency.

Excess fluid in the abdomen can be a common side-effect of some types of heart disease, liver disease,  or low blood protein levels that lead to fluid leaking out of the blood vessels.

Other potential serious causes of an enlarged abdomen can be swelling or enlargement of vital organs, infection of the abdomen (peritonitis), a ruptured bladder, or a large abdominal tumor.

Symptoms that can come with it may include lethargy, weakness, loss of appetite, vomiting, signs of discomfort, and pain.

Severe intestinal parasite infestation can cause fluid build-up.

When you observe these things, you know you have a very ill dog on your hands.

Other body areas can swell up, such as legs with heart failure or swelling of the face or legs with lymphoma.

Even something as deceptively as benign as an allergic reaction with severe swelling can become an emergency in a hurry.

Related articles:
Swelling in Dogs

Further reading:
7 Medical Causes Behind Weight Gain