Cows only produce milk when they’ve recently had a baby, so farmers get their cows pregnant every year. The females become the new milking cows, and the males go into the grinder. The males aren’t used for meat because different breeds are used for milk than for meat.
It’s a little better than that, males are kept pent in too small enclosures and fed only milk until they’re too fat to move, THEN they’re slaughtered, because veal is pretty fuckin tasty