Anytime a dog refuses food and also has diarrhea it can be cause for alarm. Dogs love to eat, and when they refuse their normal meal and have diarrhea, chances are there is something going on with their intestines.
Common reasons veterinarians see puppies and dogs is due to loss of appetite and diarrhea. Puppies in particular tend to eat things they should not, which in turn can cause an upset stomach and lead to diarrhea.
The main cause for loss of appetite and diarrhea is a sudden change in the dog's food; switching foods should be done gradually over a seven-day span. Other causes include colitis, or inflammation of the colon.
Lack of appetite along with diarrhea is normal for one day; dogs, just like people, can feel a bit under the weather. Longer periods are when it becomes a concern and warrants a trip to the veterinarian to determine the cause.
When changing foods, try adding 1 tbsp. of plain canned pumpkin since this helps with both diarrhea and constipation in dogs.
When a dog has diarrhea for 24 hours or more, he needs to be seen by a veterinarian since he is likely to become dehydrated. If the cause is colitis, the dog will need an antibiotic in order to overcome the condition.