Carnivore digestive systems are short. Ferrets, cats, and dogs are all carnivores and benefit from an all raw diet. It is meant to move and digest food very quickly. When you feed a carnivore kibble, it takes longer to go through their digestive system. If you are feeding both raw and kibble, the kibble slows down the digestive system and the raw sits in the digestive tract for too long. It is kind of like when humans eat foods that cause us to feel backed up and constipated. It doesn't feel good for the ferret and doesn't provide any benefits.