check out nifty.org, in the gay -> authoritarian section there is a story called a lesson in time. It's not exactly like your fantasy but it shares enough similarities for me to mention it.

Also there are quite a few stories about slaves, and slave milkings in both the sci fi and authoritarian sections to make your head spin
I don't have any links, but it seems that people on a whole believe that production of sperm increases when the prostate is massaged. So you'd definately want that.
I don't think you would want people jacking the cows because while they would be able to learn and what not, then you are getting the men all horned up, though I suppose in theroy you could let the men fuck the cows afterward. Or you could have one cow milk another, then the milking cow gets milked after he's increased his arousal by playing with the other one.
If you're going to store them in a barn all together, then I think chastity devices, or VERY severe punishment would be need to stop them from having sex outside the milking chamber. And also to maxamize the displeasure or the chastity device, you could either have a battery operated shock cock ring which would keep the arouse, or some kind of butt plug

Butt plug could get messy though if you leave it in too long.
And while right now you may not be able to get the gov't involved in helping you recruit your cows. You could certainly find people who would willing become cows. Just make sure you dot all your i's and cross all your t's. Then make a website

make cum perfume, and cum cocktail, and cum body lotion, and cum massage oil, and cum other stuff. Trust me there are people who will buy it now.
