One of the most powerful instincts a dog has is the drive to eat. The causes vary, some are easily fixed while some will require a trip to the vet.
Illness is the most common reason a dog will lose his appetite. If Lucky has gone off his food, perform a brief examination for any obvious medical causes. Start by looking in his mouth. Dental problems can cause a dog pain when eating. It may be that Lucky’s appetite is fine but he's in too much pain to eat. Gently feel his abdomen. If it is noticeably swollen or distended, he may have a digestive problem. Examine his stools, too. If they’re markedly different from the ones you’re used to, he may have a stomach bug. If appetite loss continues for more than two days, visit the vet.
Stimuli cause different reactions in dogs. If a dog becomes stressed, he may very well lose his appetite. Moving house, travel, a new dog in the home or simply just an alteration to the daily routine may cause Lucky to feel stress.
Dogs eat more in their first year and during growth spurts. If your puppy’s appetite has recently diminished, it may be because he simply doesn’t need as much food as he was consuming. Similarly, when dogs hit old age they exercise much less, so their minimum caloric intake decreases and the risk of overeating rises. While most dogs will keep eating whatever you put down for them, potentially resulting in obesity, others have a more sensitive metabolism and will naturally moderate their intake.
Changes to Feeding Routine
Changing his food can cause Lucky to lose his appetite. The new flavors, smells and textures simply may not appeal to him. If you’ve bought him a new bowl or have started using an elevated feeding position, this may cause discomfort during eating, which puts Lucky off his dinner.
Perceived Loss of Appetite
If your dog has been stealing food, for example from the bin or from the yard, it may appear to you that he has lost his appetite when in fact he’s eating very well indeed behind your back. Persistent lack of appetite will result in weight loss, but if Lucky’s weight is constant or even going up though he's not eating from his bowl, he may have found a preferred food source.