I have a bottle calf that is now a short yearling (meaning she is just over a year old). I bottle fed her 3x a day and she had free choice access to grazing. They do not need grain at all to develop their digestive system. They are getting what's intended to them - milk. When calves are born, they nurse mama, and begin to see mama and others grazing. They never get grain and develop just fine. As you watch her more and she gets older, you'll see her graze more. Make sure she has access at that point to a good loose trace mineral. She'll do fine with that. If you do not have grass for her to graze, give her a bit of hay to play with. Very quickly she'll take to that.