Bright Red Blood

• The presence of bright red blood in a cat's feces is called hematochezia. According to veterinarian Dr. Bari Spielman, something has entered the cat's lower intestines closest to the rectum and caused damage. This could be a poison, bacterial infection, intestinal worms, cancer or even a foreign object. If a cat swallows a small sharp rock, for instance, it could pass all the way through to the lower intestines or the rectum before causing a wound which passes out with the stool. The blood is close enough to the rectum so that it does not have time to be digested by the cat's body. Constipation may also cause bright red blood smeared over the stools. Straining to produce small, hard stools tears the cat's tender rectum and causes the bleeding.
  
  

Black Stools

• The normal color of a cat's stool could be dark brown but black, tar-like stools (called melena) are a cause of alarm. Black, tarry excreta means that the cat's body has digested blood. Something has entered the cat's body and caused damage to the beginning of the digestive tract so that the blood leaked out by the damage has had time to go through the cat's digestive system. The causes can also be a foreign object, cancer, bacterial infection, poison or the side effects from prescription drugs. Whatever it is has been in the cat's body for a while, so the cat may be ill. Call the vet at once, especially if the cat is vomiting, losing weight or having coordination problems.
  
  

Bloody Spots or Stripes

• According to the Cat Owner's Home Veterinary Handbook, the presence of a few spots or thin stripes of bright red blood is usually not a cause of alarm if the cat is otherwise acting in his normal behavior. The cat could have had hard bowel movements which cause minor injuries to the rectum. But if the bleeding does not stop, call the vet. This could be the sign of an infection. The cat could have eaten prey that were already infected with the juvenile or cyst form of protozoa that multiply in the cat's digestive tract. These cysts take root in the lining of the cat's digestive tract and multiply. Their invasion irritates the lining of the digestive tract and causes the bleeding.