As Dun mentioned.......8 weeks is optimum for weaning, and everyone is different , just as each calf is.... a good starter should be offered about a week after birth. A GOOD starter with high protein and fat content, along with medication to prevent coccidia.
But actually the calf is the one that will tell you when it's ready to wean. again as Dun mentioned. when it is consuming at least 2 pounds of grain a day, you can consider weaning.... and you can either cut back the feedings, cut back the replacer and substitute more water, or cut him cold turkey, which some do, but I would not suggest, as it is a stresser in it self.
We wean our calves at different times. We kinda put values on our calves........ we wean the least valuable calves, such as Jersey bulls at 4 weeks if we can.( and yes they do pot belly for a while) The Holstein bulls at 5-6 weeks, heifers at 8 weeks,and our beef breeds on the bottle up to 8 weeks. or even more.
Our incentive is to turn over as many calves and open our hutches up to new ones as quickly as we can. Every one has a different type of operation.
but it is between you and your calf. Good luck! :cboy: