A little amount of blood is not something uncommon in a dog's stool. However, if you notice heavy discharge of fresh blood or blood clots, you need to tackle the matter with the utmost care. It may be an indication of some serious hidden disorder occurring in the body of your pet dog. Some of the accompanying symptoms of bloody stool are dark stools, loose motions, vomiting, increased urination, pale gums, lethargy, excessive thirst, and loss of appetite and weight.