The diarrhea can be acute or chronic with acute diarrhea being more common in puppies and young dogs although it can affect dogs of any age. Acute diarrhea starts suddenly and tends to last anywhere from a couple days to a couple weeks. It is important to understand that diarrhea is a symptom, not a disease in itself and is a normal response to the imbalance of the absorptive, secretory and motility actions of the gastrointestinal tract.