Most people wean at six months. If you wean before sixty days the calf will suffer and if you do not wean before sixty days before the next calf, the cows udder will not get its necessary rest and she will not milk properly for the next one. The first week the calf gets all energy from the milk, and at six months only ten pecent of the energy is from the milk. So then it is time to feed the calf stronger food than his mother should have, and time to wean.