Dairy calves are separated from their dam soon after they are born in most dairy operations. In some there is no contact between calf and cow for health related reasons, such as preventing Johne's disease. The main purpose of separating dairy cows from their calves to allow collection and selling of milk. The calves are then fed colostrum from the dam for the first few days, and then milk replacer. Dairy calves do not have ab libitum milk like beef calves. By limiting the amount of milk the calves receive it caused the calves to consume more feed which leads to faster development of the rumen. Dairy calves are usually weaned off milk early, usually at 4–8 weeks of age.