A dog that has diarrhea but is in good spirits may be caused by catching a cold, improper diet, a cold, internal parasites, or indigestion. It may also be caused by a viral infection in the early stages. You can first feed the dog some probiotics, and then some Eat light and easy-to-digest food and observe for two days to see if there is improvement. If there is no improvement or other complications occur, it is best to send the dog to the pet hospital for examination and treatment immediately.