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Predicting and Promoting Bull Fertility

Breeding soundness exams return $20 for every $1 invested.

RUIDOSO, NEW MEXICO (Aug. 30, 2018) — The title of this synopsis suggests that scientists have it all figured out – that they know all there is to know about predicting the fertility of bulls. According to reproductive physiologist and University of Idaho researcher Joe Dalton, that just isn’t so.

“Studies suggest a benefit-to-cost ratio of $20 for every $1 invested in the BSE,” reported Joe Dalton, University of Idaho.

“We don’t know everything. We don’t know all the reasons why some bulls are fertile and others are not. At best, we have a partial list of attributes of fertility,” said Dalton, during the Applied Reproductive Strategies in Beef Cattle Workshop hosted Aug. 29-30, in Ruidoso. “We don’t predict fertility as much as we estimate fertility,” he added.

While scientists don’t understand all of the reasons why, they do know that semen quality varies among sires. Dalton said differences can be due to compensable semen traits, which affect the viability or morphology of sperm cells, making them unable to compete for fertilization of the ovum (egg). Compensable traits may be overcome or minimized by increasing the number of sperm delivered during insemination. According to Dalton, reputable semen sources routinely adjust the artificial insemination (AI) dose when compensable deficiencies are known.

Dalton explained that low fertility also may be the result of uncompensable traits, which often result from damaged DNA. As a result, a bull’s semen may contain unacceptable levels of abnormal sperm cells, which may be capable of starting the fertilization process but unable to complete it. Dalton said bulls known to produce sperm exhibiting uncompensable sperm traits should not be collected and used for AI.

Dalton cautioned producers to source semen only from reputable firms. He also warned producers against falling for semen sales advertising based on a “double dose” of semen. Uncompensable traits cannot be overcome by increasing the number of sperm cells when the sperm is incompetent.

“Doubling the dose won’t fix it,” emphasized Dalton.

For promoting fertility among breeding bulls, Dalton reminded his audience of the importance of conducting a breeding soundness exam (often referred to as a BSE). While some producers claim to always have their bulls semen tested prior to turnout, Dalton warned that a semen test really isn’t good enough.

A complete BSE includes semen evaluation for sperm motility and morphology, as well as measurement of scrotal circumference. However, a complete BSE also includes a physical examination of feet, legs and eyes, as well as the testes, epididymis, penis and prepuce.

According to Dalton, BSE results will classify bulls as: a) a satisfactory potential breeder, b) an unsatisfactory potential breeder, or c) classification deferred. Classification as a satisfactory potential breeder does not guarantee the bull is currently a satisfactory breeder, or that he will be in the future. The BSE outlines minimum standards that must be achieved, in addition to passing a physical exam, but it does not evaluate a bull’s libido, which is a necessary trait of satisfactory breeders.

Dalton recommended bulls undergo the BSE at least 60 days prior to breeding season. Bulls of “classification deferred” status may improve with time, so early evaluation allows sufficient time for repeating the BSE prior to turnout.

According to Dalton, a semen test alone is not sufficient because some bulls may fail the physical exam. He cited an example where more than 50% of evaluated bulls were classified unsatisfactory because they failed physical examination. Economically, performing the complete BSE routinely is a prudent practice.

“Studies suggest a benefit-to-cost ratio of $20 for every $1 invested in the BSE,” reported Dalton.

For details on Dalton’s presentation — including the proceedings, PowerPoint and video of his presentation — visit the Newsroom at

Editor's Note: This article was written under contract or by staff of Angus Media. To request reprint permission and guidelines, contact the Angus Media editorial team at 816-383-5200.