When you're harvesting bull semen, the general method is to shove an electrified probe up their rear until they provide the goods. (That's the real money in cattle, apparently--top beef stud semen is worth many times its weight in gold.)
Now, I think there's a limit to how often a human male can ejaculate and have viable sperm--if memory serves, it takes a few days for a sperm to grow, and so a guy could conceivably (no pun intended) ejaculate sufficiently that they would run through their available sperm until a new crop came out of the testes. I could be on crack on this one--my sex ed classes were in a public school--but such is memory. (NOT that you would rely on this for birth control--sweet jesus--but just that there's only so much swimming space in the testes. For all I know you'd be ejaculating dust at that point.)
Now, the question that arose is about bulls. Presumably you wish to maximize your bull semen harvesting, but as the key bit with bull semen is viable sperm, how much down time does a bull get? Is he getting a prostate massage every six hours come hell or high water, or does he work one day a week and spend the rest of his time working on his novel?
Since somebody's gonna ask why I want to know this, the answer is simply "It came up." I have no plans of getting into the lucrative field of bull ejaculate any time soon, I assure you. Really.
*And by "failing me" I mean "I don't want to google some of these terms."