There are many others you could try, including Hills k/d
diet. You can also add things to the prescribed
diet to make it tastier, such as a teaspoon of all-natural honey, plain unsweetened yogurt or a desertspoon of cooked cabbage. All these additives are useful in different ways.
I am assuming the Royal Canin is the tinned variety - NOT the dry variety? If it's the dry variety, let me know.
If you haven't already read it, try having a look at my article:
http://www.infobarrel.