I’d say it is absolutely not caused by the raw you are feeding, but more than likely a genetic preponderance in your dog to have kidney issues. My one critique would be the quality of your protein. I’d choose something that was naturally low fat like rabbit. And I personally don’t care for chicken as a protein source, given the way it is processed in this country. Actually, beef as well…Lots of factors may contribute to his high BUN levels. I don’t think it’s the raw diet, but moreover your protein choices and possibly your dog’s predisposition to kidney problems.