Dog Anus Problems and Infection Rectal or anal bleeding in dogs can be a result of different factors. Most often, problems of the anus, rectum or colon are responsible for it. Most cases of bleeding occur due to constipation, colon inflammation and rectal inflammation. Inflammation of the colon is also known as colitis and is known to cause . What I usually do is have one of my technicians hold and calm the dog and then I gently put a finger into the anus and see if I can express anything out of the sac. Sometimes, if this is an abscess we can empty out a lot of the debris inside which really speeds up . Proctitis, conversely, is the inflammation of the dog's anus and the lining of the rectum. Although inflammation of the colon and rectum can occur in any breed of dog, Boxers seem to be particularly susceptible to this condition, and will usually show clinical signs by two years of age.