The ideal time to wean depends on what you're doing. Large scale dairy farms typically separate calves from cows after a couple of days (after they have had their dose of colostrum) and feed the calves on excess milk from the vat. As this is extra labour, farmers aim to wean calves as early as possible, at around three months. By this time the calves' rumen will have developed enough so that they are getting adequate nutrition from grass and a grain ration. In beef cattle, the calves are left with their mothers for between six and nine months, they will be weaned early if there isn't enough feed in the paddock to support a lactating cow, and often the calves will then be sold to be fattened on another property. In beef cattle the process is usually to remove the calves from the cows and keep them in a yard for a couple of weeks, with hay to eat, and then either sell them or keep them in another paddock, away from their mothers.
On a small farm, you can do whatever suits you, as long as a pregnant cow is dry within about two to three months of calving so that her body has a chance to prepare. With our first bottle fed calf, we were buying milk powder for him, so we weaned at 3 months when the bag of powder ran out. With Molly, it suited us to have her taking milk from Bella too, so that we could occasionally milk Bella when we wanted to, so we let her stay with Bella for over a year. This hasn't done her any harm, she's grown up big and strong, with lovely straight horns.
Our main concern after weaning was that we wouldn't be able to put Bella and Molly back together in the same paddock without Molly sneaking a drink. After Bratwurst was butchered, we decided it would be nice to have all the cattle back in one paddock again, so we thought it was worth giving it a try to see what would happen. We let Bella and Molly into the same paddock just before feeding time. When Molly was finished with her grain, she went over to Bella and tried to get a drink, just like she used to do after dinner, but Bella gave her a little warning kick, and we haven't seen her try again since. The next test will be when the new calf comes, if Molly feels that she is entitled to milk again at that time.
The main thing we have learnt is not to be restricted by the production models on large farms. They are doing what they need to do in order to make money. We have some other aims, including having milk available when we want it and growing up a strong calf, so the way that we weaned worked for us and for our cattle. And now we known that it is possible to put weaned animals back with their mothers, we will try it again in future. It may not work for all cows, they have to be strong enough to not let an older calf drink, but it is worth a try.
How do you manage weaning at your place?