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Copyright © 2015
Angus Journal

Using Natural Service:
Bull Management Considerations

FORT COLLINS, COLO. (Dec. 3, 2008) — It isn’t new, and it isn’t rocket science, but understanding the dynamics of bull fertility and management of breeding bulls is fundamental to sustaining a successful breeding herd. During the Robert E. Taylor Memorial Symposium in Fort Collins, Colorado State University Extension Veterinarian Roger Ellis said the fundamental goals of natural service breeding programs are threefold:

A breeding soundness exam is not a lifetime guarantee a bull will perform to a producer's expectations, said Roger Ellis, Colorado Extension veterinarian.

Producers commonly have high expectations of bulls classified as “satisfactory,” following a breeding soundness evaluation. However, Ellis reminded producers that the standardized breeding soundness evaluation is a risk management tool that assesses testicular development and health, spermatozoa quality and quantity, and a bull’s physical capability and soundness to accomplish mating. Applied correctly, the procedure identifies faults or weaknesses that would contribute to subfertility at that point in time. It does not predict whether a bull will be a superior or inferior breeder.

"It is not a life-time guarantee that a bull will meet expectations,” stated Ellis. “Fertility is a dynamic condition. It is in a state of state of change, on a day-to-day basis.”

The evaluation does not predict a bull’s eagerness to mate (libido). Nor does it reveal how the environment and management might influence the actual performance of bulls previously determined to be potentially satisfactory breeders. The age and experience of bulls and herd social hierarchy influence breeding performance, as does the bull-to-female ratio.

“Luck plays a role too — whether or not a bull remains injury-free during the breeding season,” Ellis added. “Mating is a hazardous occupation, and the most common cause of removal from a natural mating situation is injury.”

Ellis urged producers to observe and evaluate the reproductive and physical soundness of bulls throughout the breeding season. They should be observant of changes in libido and mating activity, and apply bull rotation or replacement as necessary. When natural service is used in conjunction with an estrus synchronization program, producers should be even more vigilant.

The Robert E. Taylor Memorial Symposium is conducted by Colorado State University every other year to provide current, research-based information for improving profitability in the beef cattle industry. The ARSBC program was developed by the Beef Cattle Reproduction Task Force to improve understanding and application of reproductive technologies, including AI, estrus synchronization and factors affecting male fertility. In 2008, CSU and the Task Force collaborated to provide the Dec. 2-3 symposium in Fort Collins. To listen to this presentation, view the accompanying PowerPoint or view other presentations from the symposium, visit the newsroom at

— by Troy Smith

Click here for accompanying PowerPoint as a pdf file (928 KB).
Click here to listen to the audio (5.8 MB mp3).

Editor’s Note: This article is available as a news release to redistribute per an agreement between the symposium hosts and Angus Productions Inc. Click here to submit a request for a high-resolution photo of the speaker. For additional information visit the newsroom of