Actually, prey feed can make a difference, because there are some ingredients that the snakes can't metabolize like red dyes commonly used in dog food. Your best bet is to either make sure you're getting your prey from a good source (such as www.rodentpro.com or www.miceonice.com or www.gourmetrodent.com for example), or to raise and feed them yourself with a diet consisting of fresh fruits and veggies, rodent lab blocks, undyed dog food (such as Ol' Roy), and other healthful foods.