Agreed Droid, for working ferrets a higher proportion of uncooked fat is needed as ferrets can convert this to energy quicker than protein. Protein is used to build up muscle and stamina. If your ferrets are lounging in a cage etc. then a lower fat content so that they don't get out of shape. Whilst dry foods are ok they do put a strain on the kidneys due to the higher volumes of water that a ferret has to consume to gain enough moisture. Raw meat is best, rabbit, chicken, and game birds (including liver, kidney etc), odd bits of lamb, beef, venison and mutton.
Andrew