At the moment P and S won't eat anything but Whiskas Chicken Supermeat. Unfortunately, my local shop ran out of it a few days ago and I had to give them Felix. You should've seen the looks of disgust! They nibbled, walked away, then went back a few hours later for another disgusted nibble, but wouldn't finish it. I let this go on for a couple of days then scoured the area for a shop which sold their fave. I knew they weren't ill, just put out by the food-type.
Ela, the general behaviour of Tango suggests that he was ill - hiding etc. Cats often have hot ears when they have a temperature (unless they've been sitting infront of a warm fire!).
I think there's a difference between illness and fussiness.
Your point about the change of ingredients brings to mind a huge row one of my friend, Rebekah, had with Whiskas. She had 5 cats at the time (only 4 now
) and they'd all started refusing it. The smell of the food had changed also. I tried the variety and mine wouldn't touch it; so she phoned the company, who admitted to changing the recipe. Not being a person to take things lying down, she demanded her money back!