At a week old you can also start offering pellets. I believe its called menna , its pellets with milk in them . You only start with a hand full though, over feeding can make them sick, just like too much milk. Also at 7-10 days they can eat hay. My father in law was a vet for 45 years, and we have a cattle farm, am dealing with the same thing right now with a little 3 day old heifer. I feed her 2 bottles a day, supplemented by water in the bottle if shes still hungry, and have small amounts of hay out. Its also good to treat with amoxicillin 3 cc once a day for 5 days, just to prevent them from coming down with something or treat if they do.