Hi there, I have a Rhodesian Ridgeback puppy (7 months old) who won't eat properly. I will buy a new type of food, and he will eat it like he hasn't been fed for weeks, for a week or so, then he will start turning his nose up at it. What I have found is that if I fill up a couple of Kong toys with ANY dog food, he will scoff it. It's as though he is bored with just having the food put in front of him, but actually enjoys working for his food. It's worth a go! Another thing I sometimes do, is spend time making a game out of eating, for example if he is having dried kibble (which he would leave for days in his bowl), he will eat the lot if I hold the bowl and throw it to him, or place individual bits on the floor in a pattern and make him wait to pick them all up.
I think dogs are programmed to work for their food, and my pup certainly seems to enjoy his grub when he has to work for it, otherwise he just won't eat!
Hope this may help.