bloody stool in dogs

Question
I have 3 dogs ranging in age from 3 years to one year old.  They recently showed signs of having blood in their stools.  I haven't changed their diet so I don't think it is the dog food.  Can you please tell me what might be the cause of this?

Answer
If all three of them suddenly developed blood in their stool, it could be a viral intestinal bug that affected all of them at once. It could also be the food- did you open a new bag of food recently? There could have been something wrong or different with the new bag of food, even if its the same brand. They could all also have worms, especially tape worms. Try giving them a can of pumpkin filling (like for pies) and some cooked plain white rice to help flush their system out and start over again.

If it continues after that, a trip to the vets may be a good idea :)