1. Gastric Dilation-Volvulus (GDV).

GDV, also known as bloat, is a life-threatening condition in dogs where the stomach becomes distended with gas or fluid and can rotate on its axis. This rotation can cut off the blood supply, leading to tissue damage. In some cases, the initial stages of GDV may not be painful, but as the condition progresses, it can become excruciating.

2. Ascites.

Ascites are the accumulation of fluid in the abdominal cavity. It can occur due to various reasons, including liver disease, heart failure, kidney problems, or certain cancers. The swelling caused by ascites may not always be accompanied by pain, especially in the early stages.

3. Tumors.

Non-painful abdominal swelling can be caused by the growth of tumors or masses in the abdomen. These tumors could be benign or malignant and may arise from the organs or tissues within the abdominal region

See What You Should Do>>>>https://heathlinecare.com/dog-swollen-stomach-no-pain/