Watch the bulls closely
The first of May is typically a date planned for turning bulls into the breeding pasture with spring-calving adult cows. A good manager keeps an eye on his bulls during the breeding season to make sure that they are getting the cows bred. Occasionally a bull that has passed a breeding soundness exam may have difficulty serving cows in heat, especially after heavy service.
Bulls that cannot physically inseminate cows or bulls with very low libido (desire to mate) can be detected if observed closely.
On rare occasions, bulls may have physical problems with the reproductive tract that prevent them from successfully breeding females. Such problems can best be detected by observing bulls while they work.
Therefore producers should (if at all possible) watch bulls breed cows during the first part of each breeding season.
If problems are apparent, the bull can be replaced while salvaging the remainder of the breeding season and next year’s calf crop. Likewise a small proportion of bulls can wear out from heavy service and lose interest. These, too, will need to be replaced. The greater the number of cows allotted to each bull in the breeding pasture the more critical it is that every bull be ready to work every day of the breeding season.
Injuries to bulls during the breeding season are relatively common. When a bull becomes lame or incapable of breeding, because of an injury to his reproductive tract, he needs to be removed from the breeding pasture and replaced with another bull. — Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist