[kaybe]

There is a rare practice where you (for example) separate them just for the night and milk the cow in the morning. During the day, the calf will take the milk. Yes, you lose a lot of the milk that way, but apparently your vet bill also goes down because the calf will be healthier.

Another option is to pool several calves to one cow and foster them for more natural suckling behaviour. This is a bit more common.

Interestingly, apparently cows can choose to either give the milk or not which makes the logistics more complicated.

I can currently only find sources in German for this though ('muttergebundene Kälberaufzucht' / 'ammengebundene Kälberaufzucht').