Veterinarians classify diarrhea as either acute, which means a single episode in isolation, or chronic, which refers to a protracted episode that lasts longer than 3 weeks. Chronic diarrhea can also refer to several episodes which occur close together, even if feces are normal in between these episodes.
Usually, acute diarrhea is more common in young animals – either puppies and kittens or young adult animals. Chronic diarrhea, on the other hand, occurs more frequently in older dogs and cats. That being said, acute or chronic diarrhea can be seen in pets of all ages.