I have had some people tell me that since the two are digested differently it could cause problems? I've been told that raw digests more quickly than kibble so mixing the two can cause the raw to linger in the digestive track with the kibble and build up bacteria. Hopefully some raw feeders will chime in soon. I used to feed them together before I was told differently. I never had any problems, but I try to split them up now just in case. My pup apparently has a lead gut, so he might not be the best example.