[LunarBerry]

We rotate our dogs' diet every so often (about 1-3 months, give or take, like you) and usually between a few brands/flavors. Found that if we keep them within a certain number to change with, they usually have no problems when switching over as much as if they got something totally new. (also we generally add the newer food to the bin that has some of the older food left so that it'll mix)