Observe bulls closely as breeding season begins

Apr 19, 2010
by WLJ

Another title for this article could very well be: “A lesson nearly learned the hard way.” Quite a few years ago at the Eastern Oklahoma Pasture Research station, we were involved in a field study using synchronized mature cows in a natural breeding pasture. At the time, not much was known in the scientific literature about cow:bull ratios when estrus synchronization was involved. Therefore, we observed very closely as a mature experienced bull was placed in a pasture full of 25 cows synchronized to come into heat together. He had passed a breeding soundness exam. What I observed was a lesson for all commercial cow/calf ranchers AND had nothing to do with the original purpose of the study. The bull selected to mate with this group of heat-synchronized females could not, or would not, physically inseminate any of them. He was successful at impregnating cows the year before, but something had changed since the previous breeding season. Fortunately, we observed the problem and found a replacement bull within hours of the start of the breeding season. In many herds, this bull may have caused a partial or complete loss of a calf crop.

A good manager keeps an eye on his bulls during the breeding season to make sure that they are mounting and inseminating cows. Occasionally, a bull that has passed a breeding soundness exam may have difficulty serving cows in heat, especially after heavy service. Inability to complete normal service and low fertility are more likely to be detrimental to calf crop percentage than failure to detect cows in heat. Many physical problems or low semen quality can be detected by breeding soundness exams. Low libido or inadequate sex drive probably will not be detected before the breeding season.

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. No one can watch all of the bulls all of the time, but the “lesson learned” was to be as observant as possible as bulls are turned out to the breeding pasture this spring. — Glenn Selk, Oklahoma State University Extension Cattle Reproduction Specialist