It’s well known that dogs love their tucker, so if Fido is off his food, there's likely to be a good reason. Has he had to get used to new surroundings? Some dogs get nervous and uncomfortable in unfamiliar places - like new homes or on holiday. Others get travel sickness. Some are just picky, or won’t eat in places they feel uncomfortable, such as around another dog or from a bowl sitting somewhere that makes them uneasy. So if your dog’s appetite was fine until some sort of change was introduced, this might well be the cause.