Dry Food Tummy Trubles

What would be the first ingredient to avoid of Blue Buffalo Indoor Chicken and Brown Rice formula causes one of my kitties to have extremely loose/stinky stool?

He is fine when he eats just wet chicken or beef or fish foods. I can't always be home for meals times so i have to feed both.

Well, I finally found a place that sells Wellness and Merrick (sp?) so I decided to go with Welness indoor formula (which they are LOVING)for the dry and I'm trying out a few cans of wellness wet... we'll see