Spud;

I had the same kind of problem I just kept trying different mixtures when needed. I keep one of those hand blenders and a metal cup in the tack room and just through in whatever I have for my old guy.

Sometimes a fresh apple, Carrot or even used a granola bar once. That way he never knows if he is getting a treat or the bute. Sometimes if the items isn't strong enough he will try and refuse it and I have throw in some karo syrup. Works everytime. You know when we get older we like the treats!