Causes of bleeding in dogs:

1. When the dog’s sexual organs mature at about 8 to 10 months, menstruation will occur, once in spring and summer. The bleeding will last for about 11-14 days.
2. If the dog's lower body bleeds during pregnancy, it is likely that the abdomen has been hit or impacted, leading to miscarriage.
3. Female dogs in estrus will also experience lower body bleeding, which generally lasts for 7-14 days and is a normal physiological phenomenon.
4. If dogs are mating, the male dog’s penis is too large and damages the female dog’s vagina, which will also cause bleeding.
5. If the dog suffers from urinary tract infection, prostatic hypertrophy, urinary stones and other diseases, it will also cause bleeding, and the dog needs to be taken to the pet hospital for examination and treatment in time.