I have apparently very hearty rabbits. We just were buying whatever was the least expensive good food at the time so they got theirs changed about every week because I had a lot of rabbits at the beginning and they were going through a lot of food. At one point I mixed some of the old food into the new bag thinking that I would change it gradually. The problem was the old food had molasses in it and the new food did not so when they got to the new food they did not like it and they would dig and throw out all the new food onto the ground looking for the sweeter old food just like cats do. So I started to just wait until they completely emptied their feeder and then put the new food in so they got a jolt of a brand new type of food to their system and it didn't bother any of them including the tiny babies. I don't recommend this because I don't know that much about rabbits and everyone else seems to think this isn't a good idea but it certainly didn't bother my rabbits in any way. They also get a lot of scraps and banana peels, yard clippings, fodder, BOSS, oatmeal, tree branches, bamboo, whole wheat, hay and straw (oddly, they seem to like the straw better than the hay). The kits start eating all the same as their mom as soon as they hop out of the box. Through three litters I have had no issues whatsoever and all the kits have been extremely healthy and happy.
Liz