Same with our dog, Benny (Tibetan Terrier possibly crossed with a spaniel of some description). Boundless energy, but funny with food. Correction: funny with his own food. We have to cycle through a couple of different brands of dog food (Purina, Royal Canin) because he’ll eagerly eat it for a few weeks, then will suddenly stop eating and look immensely disappointed whenever we put his dinner down. We just have to play hardball and let him know that he’s not going to get roast chicken on demand. A dog won’t let itself starve, and our vet said only to worry if he doesn’t show an interest in food for over three days.
We normally feed him half of his food in the morning, and half in the evening. Recently he’s been leaving his morning feed and eating it in the evening (we don’t give him his evening food until he’s had his breakfast), but yesterday discovered that Royal Canin Cocker 25 becomes DELICIOUS if you put warm water on it. I give it a week before he realises he’s been conned! 😛
We also put in a bit of chopped carrot now and again, as Benny has… er, gland issues….