It's hard to keep your cat or dog psyched for every meal. After awhile, they're bound to tire from the same ole, same ole, no matter what they eat. Even my dog, DJ, a lucky terrier who feasts on great stuff like bison, kangaroo, salmon and my mother's pot roast, gets blase about his food.
Tough on him! I know that he doesn't have any allergies and that his health is excellent, so there can't be a problem with what I feed him. He's just being difficult and picky, something I won't stand for it.
Most of the time, a dog or cat's indifference towards a healthy meal is a behavioral issue. He could be using that tactic to gain more attention, or to test you as pack leader. Just don't give in and never ever lose control of the menu.
Remember: You're the alpha, your pet follows. In the wild, there's no discussion whether the alpha's pack mates feel like eating deer instead of elk. They chow down what they catch, no discussion.
All this to say is that I want my dog to know that I'm the pack leader and am in total control the menu. If he feels the odd pang of hunger - that's okay. My tactic for gaining his unconditional appreciation of his diet? I reduce his portions on weekends to about 75% of what he gets during the week. Come Monday morning, my wiry terrier is jumping for his food, attacking his bowl of raw food as if it's still alive.
Your cat dog may not realize his good fortune of having you as his compassionate and responsible owner, but if you give him a taste of hunger you will never have a picky eater.