How is semen collected from a bull?

A bull (one that is already halter-broke, and one that has excellent genetics to be used for breeding cows) is led, by a lead shank attached to a nose ring, to a teaser steer. The teaser steer has just been implanted with estrogen hormones. This actually fools the bull into thinking that this steer is a female in heat. The bull sniffs the bull briefly, then mounts him to breed. By that time someone else is standing by, out of the bull's sight, with an Artificial Vagina that is designed to collect semen from the bull. The AV is temperature-controlled (which is a stimulant for the bull to ejaculate), so when the bull's penis is quickly inserted into the AV, he will ejaculate in there instead of in the teaser steer. Semen collection only takes a few seconds, but may have to be done repeatedly in order to obtain enough samples to be used for Artificial Insemination.