Applications of Technology
in Bull Reproduction
FORT COLLINS, COLO. (Dec. 3, 2008) — Research continues in an aim to learn more about improving bull semen to ultimately increase bull fertility and improve herd genetics, Jim Graham of Colorado State University told participants at the Robert E. Taylor Memorial Symposium: Applied Reproductive Strategies in Beef Cattle Dec. 3 in Fort Collins. Graham is a professor in the Department of Biomedical Sciences at CSU.
Graham emphasized that cow-calf producers should take heed of breeding soundness exams (sometimes referred to as BSEs) and the information they provide to evaluate bull fertility. All three components of the exam — the physical exam, the health evaluation and the semen analysis — are important.
Graham suggested producers cull bulls that fall into the lowest 15%-20% of the exam categories.
“Remember, the most important thing is fertility and getting cows bred,” he said. Thus, culling bulls based on BSE results, such as a small scrotal circumference or low motility, is a step toward improving herd fertility. “This is a very cost-effective approach,” he added.
Graham acknowledged there are still advancements that need to be made in the process of semen analysis. Sperm can be infertile for a number of different reasons, but current lab assays only evaluate a few characteristics. As an example Graham said, “We can identify poor-quality semen samples, but we can’t identify high-quality [samples].”
To that end, he reported that research is ongoing to develop new assay methods. One current project looks at chromosome defects. Another new method, which is called the Fourier Harmonic Amplitude, evaluates sperm morphology and then enters it into a computer database to get a prediction line of the quality of the sperm.
Additionally, research efforts are continuing to learn more about the freezing ability of semen. Graham noted that because the dairy industry has worked primarily with genetics produced by artificial insemination (AI) for the past 60 years, semen quality and freezing characteristics of dairy bulls is much better than that of beef bulls.
As more is learned about freezing semen from stallions, some of that information may be applicable to beef cattle, Graham said. For example, the horse industry is using diluents with different compositions because some horse semen freezes better than others and that can vary with the type of diluent used.
Different diluents may also be used more in the future for beef sires, Graham predicted. Adding cholesterol to the bull sperm membrane has been found to increase viable sperm significantly. However, this practice appears to lower fertility. Thus, some trials are looking at insemination occurring earlier to try and increase the window of time for fertilization.
Lastly, Graham mentioned the status of sexed semen in cattle. He explained that the only way to sex semen reliably is based on the different DNA composition of the X and Y chromosomes — the X chromosome is 3.8% larger than the Y. “That’s not very much,” Graham noted.
A flow cytometer is used to stain and sort sperm into X- or Y-bearing categories. Graham reported sorted sperm are very different than non-sorted sperm due to the pressure of going through the flow cytometer.
“Sex-sorted cells swim differently; die more quickly and have more damage,” he noted.
Because of the fertility differences in bulls, semen from some bulls cannot be sorted, Graham said. “Some don’t take the stain through the sorting process or because of the added damage to the cells after sorting, they won’t freeze.”
CSU research has shown that sexed semen is safe to use in breeding programs and that there are no differences in calves born from sexed semen compared to calves born from non-sorted semen, but Graham wants people to understand that the sorting process does limit the amount of sexed semen available.
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 Graham’s presentation, view the accompanying PowerPoint or view other presentations from the symposium, visit the newsroom at www.appliedreprostrategies.com.
— by Kindra Gordon
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 www.appliedreprostrategies.com.