Morphy (aged >11½) has never been a great enthusiast regarding food. He eats it, but has never been in the habit of clearing his bowl, and quite often the food waits there for several hours before he bothers to try it. He has two meals a day, hitherto consisting of ¼ tin of Waitrose meat, and a scoop of Beta "Sensitive", which allegedly contains salmon and rice. If he has some left from the previous meal, we don't give him a full portion, but just top up.
When Mrs. Wow and I were in Pets at Home last week, on the lookout for another bag of his usual, we saw a variety that we hadn't spotted before, Arden Grange Senior, which is, allegedly, made of chicken and rice and has a high level of joint supplements (old Morph has arthritis). It was a bit cheaper than his usual. We bought some.
Since moving over to the new food, he has become much more enthusiastic about his meals. He clears his bowl every time as soon as he is given it, and nags for food more than he ever did. I reckon if we are not careful he might put on weight.