Thank you for the reply, I messed up by giving her the new food on its own, not mixed at all, she now has an upset stomach.I mix my foods. Just throw two bags into the same air tight container and shake it up. The only problem with mixing foods would be identifying which is causing problems if there are problems (i.e. runny poop or vomiting). While I haven't run into that myself it is something to keep in mind.