Stress on the cow will actually cause her to hold her milk and that can cause mastitis. You will not stimulate more milk by causing the cow to hold her milk for any period of time. The calf will be bawling, the cow will be bawling, and everyone will be trying to get in with the other. Then you will wind up with cattle getting loose and torn up fences. Anytime a calf is stressed, it compromises it's immune system and that allows more opportunity for calves to get sick.
The comment about genetics, environment, and feed is right to improve the milking ability of an animal.
A neighbor gets his calves separated from his cows and locks them in a catch pen for another neighbor to come help band/castrate/cut them; the next day and sometimes the day after.... They will scream all night long and the cows are just outside the fence screaming all night long. Why in the world he just doesn't get them in with their calves and just cut the calves out to be worked the next day I will never know. Then, he has trouble getting them to come back in the lot because they associate it with something "terrible"...
I understand that it is supposed to be a method to get them to cycle.... no thanks, I want my animals to want to come in when I want them, not think that I am going to do something mean and terrible to them.