The reasons that cause dogs to have bloody stools are as follows:

1. Gastrointestinal and visceral diseases: When visceral diseases such as gastroenteritis or pancreatitis develop seriously, it may cause dogs to have bloody stools. These diseases are often accompanied by other symptoms, such as listlessness, loss of appetite, vomiting, elevated body temperature, and abnormal color of the conjunctiva.

2. Constipation: Dogs may suffer from unreasonable diet or physical problems. (For example, you don’t like to drink water, your daily dietary fiber intake is not enough, you don’t like to exercise, etc.) Constipation occurs. When a dog's stool is dry and hard, it may be difficult and laborious to defecate. In severe cases, it may damage the intestinal mucosa and cause bleeding.