How long can a cow give milk for after a calf and can a cow give milk without having a calf

A person asks. How long can a cow give milk for after a calf and can a cow give milk without having a calf

Here is my reply: I have been involved with dairy farms for 23 years on farms that have cow protection principles. That means farms that don’t kill their cows at anytime throughout there life.
It was very common for me to find cows that gave milk without even having a calf. In some cases I brought this into being by encouraging certain farms to try and induce cows /heifers that were showing some slight swelling in there udders. In other cases the cows were induced to give milk without even showing any signs of swelling.
Some of these cows gave 10 litres of milk each day. Exactly how many cows you can do this too has not been systematically tested from what I know.
As woman in histroy would induce themselves to give milk (as wet nurses) the cows seem to have a similar trait in that if you go through a milking regime with them they will start to reciprocate and produce milk.