I've done the same with mine; I usually "overlap" the last of the old bag with the first of the new bag by mixing them together gradually to smooth out the transition. If I don't have enough of the old feed to do that with, I cheat and give them extra fruits and veggies for a day or two, and have never had issues with them adjusting to the feed when it changes.That was the plan. I'm actually more concerned with switching brands frequently. Does it really matter?