Factors Affecting Fertility of Conventional & Sexed Semen
By Troy Smith, field editor
When grasping for reasons why results from artificial insemination (AI) were poorer than expected, a frustrated producer might think his or her semen source delivered an inferior product. That’s possible. It depends on the source. According to University of Idaho reproductive physiologist Joe Dalton, however, reputable commercial AI studs and custom semen collection businesses apply stringent quality-control practices to collection and processing of semen. They typically provide customers with a highly fertile product.
That doesn’t mean product quality always remains high after a customer receives a semen order. Speaking at the Applied Reproductive Strategies in Beef Cattle symposium, Sept. 7-8 in Des Moines, Iowa, Dalton said there can be ample opportunity for semen fertility to be compromised during on-farm handling, or during the insemination process. He talked about numerous semen management and insemination-related factors that can affect the fertility of conventional semen and sexed semen.
Dalton said a common threat to fertility is improper thawing of semen. This easily happens when too many straws of semen are thawed simultaneously. So how many straws can safely be thawed at one time? Dalton says the answer is not the same for everyone.
“I recommend that you never thaw more than you can use in 10 to 15 minutes,” Dalton stated. “Think about time, temperature, hygiene and your skill level. Know your comfort zone.”
That recommendation applies to conventional semen. Dalton cautioned his audience to apply a different rule of thumb when using sexed semen. Highly processed and packaged in straws of smaller diameter (1/4 inch), sexed semen should be considered more fragile and more vulnerable to mistakes. When using sexed semen, Dalton advised thawing no more straws than can be used in five to eight minutes.
Inseminator skill also impacts fertility. Dalton said an inseminator must be capable of depositing semen past the cervix and into the uterine body.
“There is no evidence that going deeper is beneficial,” he added.
Timing of insemination also affects fertilization success. Dalton explained that, following insemination, six to 12 hours are required for sperm transport to the fertilization site and for sperm to gain the capacity to fertilize the ovum (egg). However, an ovum that waits too long and becomes "aged" may ultimately yield a low-quality embryo.
“Timing of AI is a compromise,” said Dalton, explaining that insemination following heat detection should occur near enough to the time of ovulation to maximize sperm access to the ovum, but not so late that an aging ovum waits in the oviduct. He recommended insemination within 12 hours after onset of estrus when using conventional semen.
“For sexed semen, timing is not so clear,” added Dalton. “Breeding sooner likely is better, taking into account the vulnerability of sexed semen.”
Dalton also discussed semen quality trait differences among sires. Differences can be due to compensable semen traits affecting the viability or morphology of sperm cells and making them unable to compete for fertilization of the ovum. 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 AI dose when compensable deficiencies are known.
Low fertility also may be the result of uncompensable traits which often result from damaged DNA.
Accordingly, explained Dalton, a bull’s semen contains unacceptable levels of abnormal sperm cells which may be capable of starting the fertilization process, but are unable to complete it. Dalton warned that uncompensable traits cannot be overcome by increasing sperm dosage, and bulls whose sperm is known to exhibit uncompensable sperm traits should not be collected and used for AI. It’s another reason that semen should be sourced only from reputable firms.
Dalton spoke during Wednesday’s ARSBC session focused on male fertility. Visit the Newsroom at www.appliedreprostrategies.com, which features comprehensive coverage of the symposium, to view his PowerPoint, read the proceedings or listen to the presentation. Compiled by the Angus Media editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.
Editor's Note: This article was written under contract or by staff of Angus Media. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.