Boar Fertility: It’s Not Just About Form and Speed
Most people would agree that just because you can walk to work each day, doesn’t mean you are good at your job. Karl Kerns, faculty member of the Department of Animal Science at Iowa State University, says the same concept holds true for evaluating boar semen. Just because it swims, it doesn’t mean the sperm is fertile.
For years, the thought was good motility and good morphology meant a good conception rate. But data, and experience in the sow barn shows this is not true.
“Our knowledge of science is continuously changing. As we get more data and information, like we’ve seen with COVID-19, our understanding changes,” Kerns says. “Motility and morphology is a starting place, but it’s not the end-all.”
Even though boar semen may prove to have high motility and morphology, there are still sub-fertile and infertile individuals.
“For instance, after the sperm penetrates the outside of the egg, the zona pellucida, it needs to be able to activate that oocyte so it can progress through embryogenesis, create a blastocyst and eventually create a piglet,” Kerns explains.
Proteins present in the sperm must be able to activate that new embryo. And that's something that you can’t see with a naked eye and must use advanced techniques to look at, Kerns says.
These challenges are not restricted to boars. In the bovine space, the breeding soundness exam looks at testes size and examines if the bull’s semen has good morphology and motility, but Kerns says that does not necessarily mean a bull is fertile. It is simply a starting place. The same holds true for humans.
“In humans, we know that one in eight couples suffer from infertility. We do not have good enough diagnostic tests that are approved,” he says. "Therefore, the female usually gets too much of the blame when in fact we do know that two-thirds of fertility is directly or indirectly related to the male according to the National Institutes of Health (NIH).”
The role of zinc in boar fertility
One of Kerns’ recent research studies looked at sperm zinc efflux. He and his co-authors discovered the release of zinc is critical in the fertility process.
“Sperm capacitation was first discovered in 1951, yet we do not fully understand sperm capacitation at a biochemical level. Sperm capacitation is the acquisition of the capacity to fertilize an oocyte and that happens after it has left the boar’s body. We discovered that zinc is covered on the entire sperm, head and tail, and that that release of zinc is vital for becoming competent to fertilize,” he says.
In an ongoing study, his team is looking at artificial intelligence calculations based on that zinc signature. They are studying the sperm’s ability to progress through the four unique zinc signatures and its relationship with fertility. To date, their data shows analyzing this phenomena can help make decisions of which boars to use.
How can we make progress?
Understandably, little emphasis has been placed on genetic selection for male fertility over the years. More emphasis has been placed on terminal production traits of males more so than reproduction, Kerns says. In this era of increasing use of big data and incorporating artificial intelligence, Kerns believes the opportunity is greater than ever to advance knowledge in boar fertility.
“We have not had much research be performed in this area. It's not that boar studs are not interested in implementing new technology, it's that the federal government and universities historically speaking have had a limited number of boar reproductive physiology positions to help create those technologies,” Kerns says. “Historically, the focus has been placed on sow or gilt reproductive physiology.”
He is working on biomarker assays that the swine industry can use to give decisionmakers a better idea of a boar’s fertilization competency.
“There are also technologies out there that allows one to use nanoparticles to magnetically remove bad sperm and leave the good sperm. Some of that can be adopted today, especially for various levels of production. Perhaps in the production system, you won't be using nanoparticles quite yet. But in the nucleus and multiplication system you can utilize nanoparticles from an economic perspective or even the show pig industry,” he explains. “This technology, along with many other technologies I am discussing here, were created or inspired by Dr. Peter Sutovsky at the University of Missouri.”
By utilizing these technologies and tools, Kerns believes boar stud managers can start validating boars to use in a production system, invalidating them, or flagging them for specialized andrology treatments if their genetics are marked as high value in an effort to push boar fertility towards the higher side.
What can producers do now to improve semen quality?
Don’t lose sight of the basics when it comes to getting the best results with boar semen. Make sure that the semen is put into an incubator right away after delivery – do not let it sit out in the sun or cold weather. It’s also important to rotate semen as directed. Finally, if you see agglutination, or clumping of the sperm, don’t use that dose. Even if it falls underneath the five-day recommendation, Kerns says that semen should be avoided in all situations.
He says the question of how semen quality can be improved can also be answered from a genetics and reproduction perspective. Click here to keep reading what producers can do to improve semen quality.
