A dog can be hungry for up to three or four days, and it can go three or four days without eating until you give in. At this time, it’s time to compete in will. You know, as long as there is enough water, not eating for three or four days or even longer will not harm your dog's health. But if you are not a picky eater but just have a poor appetite, it is best to go to the hospital for examination in time.