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KSU continues research on genetic prediction for male fertility

by Wyoming Livestock Roundup

Genomic technologies have been widely adopted within the beef and dairy industries, and their popularity and utility continue to increase.

Kansas State University (KSU) Associate Professor of Animal Breeding Dr. Megan Rolf discussed genetic prediction for male fertility at the Applied Reproductive Strategies in Beef Cattle Symposium held in Cheyenne on Sept. 6, 2023. 

Rolf was raised on a cow/calf operation in east-central Kansas and has been involved with livestock her entire life. She joined KSU faculty in 2016, where she now teaches genetics courses and maintains an active research program in the use of genomics for genetic improvement in livestock.

The need for continued research

Fertility is a critically important factor in cattle production because it directly relates to the ability to produce offspring necessary to offset costs in production systems. 

KSU research has established female fertility has received greater attention and has been advanced through assisted reproductive technologies, as well as genetic selection. However, improving bull fertility has been largely ignored.

Rolf explained KSU is developing new tools in male fertility.

“We’ve got to go out and collect a lot of true data,” she said. “But, the cool thing about male fertility is the data actually already exists within the industry.”

The incorporation of genotypic data into genetic evaluations is crucial for genetic improvement in the livestock industry.

She noted selection and management to improve bull fertility not only have the potential to increase conception rates but also have the capacity to improve other economically-relevant production traits. 

KSU research study 

KSU researchers published findings from a 2022 research study in the Journal of BMC Genomics, where the objective of the study was to perform a single-step, genome-wide association study (ssGWAS) on beef bull semen attributes. 

“Bull fertility is currently phenotypically evaluated with breeding soundness examinations and at artificial insemination (AI) centers, but measures of sire fertility are not currently included in genetic evaluation in the beef industry,” Rolf shared.

In the KSU study, a total of 1,819 Angus bulls with 50,624 collection records were used for ssGWAS. A five-generation pedigree was obtained from the American Angus Association, consisting of 6,521 sires and 17,136 dams. Genotypes on 1,163 bulls were also obtained from the American Angus Association and utilized in ssGWAS. 

The study classified bull fertility phenotypes to include volume; concentration; number of spermatozoa; initial motility; post-thaw motility; three-hour, post-thaw motility; percentage of normal spermatozoa; primary abnormalities and secondary abnormalities, which were obtained from two AI centers.

Research identified beef bull fertility is known to be affected by a variety of environmental factors, and the KSU research team used a forward selection procedure to identify factors which significantly affect beef bull semen attributes. 

“Factors included in the final model include variables such as fixed effects of bull age, season and year. Additional fixed effects include AI center, ejaculate number, day of the week and semen collector. The study validated bull fertility traits were controlled by genetic factors,” she stated.

Incorporating both traditional genetic evaluation approaches combined with genomic technologies has the opportunity to provide beef producers with genetic selection tools for male fertility.

Genetic evaluation

Published studies show bull fertility traits are low to moderately heritable, indicating improvements in bull fertility can be realized through selection. 

Rolf noted, “In the past, research identified bull fertility traits were low to moderately heritable, indicating improvements in bull fertility can be realized through selection.”

However, according to a 2020 research study conducted by a KSU research team – including Rolf – which was published in The Translational Animal Science Journal, genomic selection is another useful tool which can increase genetic prediction capabilities and improve selection.

Genomic prediction has an even greater impact on the prediction of polygenic traits, such as fertility, because of the ability to incorporate biological information into genetic prediction. 

While the dairy industry has been a leader in identifying genomic regions associated with male fertility traits, the beef industry has identified relatively few single nucleotide polymorphisms related to beef bull fertility.

“As genomic technology continues to advance, there is no doubt the livestock industry will benefit greatly from the genomic developments ahead,” she concluded.

Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to

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