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Copyright © 2015
Angus Journal

Factors Affecting Fertility

JOPLIN, Mo. (Aug. 31, 2011) — Getting females pregnant is the goal of any cow-calf producer’s breeding program. But reproductive failures do occur. Factors affecting fertility and, ultimately, pregnancy rates were discussed by South Dakota State University (SDSU) animal scientist George Perry during the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference convened in Joplin, Mo.

Describing the "Equation of Reproduction," Perry cited four main factors affecting fertility, whether breeding is accomplished through artificial insemination (AI) or natural service.

1) Percentage of females detected and inseminated.
With natural service, detection of standing estrus, or heat detection, is considered ‘the bull’s job,' but Perry advised managers to spend some time determining whether a bull is getting the job done. Differences in bull libido, or the desire to mate, can’t be determined by a breeding soundness evaluation. Libido can be practically evaluated, said Perry, by observing bull behavior after introduction to the cow herd.

Describing the "Equation of Reproduction," Perry cited four main factors affecting fertility, whether breeding is accomplished through artificial insemination (AI) or natural service.

When implementing synchronized AI, success often hinges on accurate heat detection. To maximize visual detection of standing heat, Perry advised observation as early and as late in the day as possible, as well as mid-day. Additional observation at midnight is better still. According to Perry, studies suggest nearly 56% of cows initiate estrus between 6 p.m. and 6 a.m. Heat detection aids such as stick-on patches indicating mounting activity can assist with this time-consuming chore. However, Perry advised visual observation, as well, to help determine the most appropriate time for insemination.

2) Inseminator efficiency.
According to Perry, natural service inseminator efficiency is influenced by the bull’s physical capability to breed a cow. Assessing this capability is the purpose of the physical examination part of a breeding soundness evaluation.

With AI, inseminator efficiency is influenced by the technician’s ability to handle semen correctly and the ability to deposit semen in the correct location. Perry advised careful attention to proper storage, thawing and insemination technique.

3) Fertility level of the herd.
Perry said the fertility level of the herd may be the hardest area to evaluate. It includes cycling status, compliance with synchronization protocols, nutrition, disease challenges and embryonic mortality. Perry focused his comments on management factors influencing embryonic mortality.

“Fertilization rates following natural service or artificial insemination range from 89% to 100%. There’s little difference,” Perry said. “Low pregnancy rates are generally due to embryonic mortality.”

Embryonic mortality can result from various stress factors, including a change of diet, explained Perry. He noted how drylot-developed heifers turned out to grass after AI may experience a period of weight loss that results in low pregnancy rates. Perry said heat stress also may increase embryonic mortality, as may vaccinating naive females (not previously vaccinated) with a modified-live virus (MLV) product near the time of insemination.

He recommended vaccinating replacement heifer candidates before and at weaning, with both heifers and cows receiving a booster at least 30 days prior to breeding.

“I’m often asked when is the best time to ship AI-bred cows,” Perry stated, noting how shipping stress also may increase embryonic mortality. “Shipping between days 1 and 4 is best, while the embryo is still in the oviduct. Or, ship after day 45 when the embryo is well-established and fully attached with the placenta.”

4) Fertility level of semen.
Whether AI or natural service is used, two of the most important indicators of male fertility are sperm motility and morphology. Perry recommended all natural service bulls receive a breeding soundness evaluation approximately 60 days prior to breeding season.

Perry warned that doing "pretty good" in each are can still result in single-service success rates below that expected. For instance, if 90% of the cows are successfully detected in estrus, if the inseminator has a 95% success rate, if the fertility level of the herd is 90%, and if semen fertility is 95%, the single-service conception rate would be 74% (90% x 95% x 90% x 95% = 74%).

Perry spoke during Wednesday morning's ARSBC session focused on management considerations influencing success in estrus synchronization and AI programs. Visit the Newsroom at to view the PowerPoint slides and the proceedings paper submitted by Perry to accompany his presentation. Audio of the presentation will be available soon.

Comprehensive coverage of the symposium is available online at Compiled by Angus Productions Inc. (API), the site is made possible through sponsorship by the Beef Reproductive Task Force, SEK Genetics, and Coverage includes summaries of the speaker presentations, PowerPoints, proceedings and audio.

Editor's Note: This article was written under contract or by staff of Angus Productions Inc. (API), which claims copyright to this article. It may not be published or redistributed without the express permission of API, publisher of the Angus Journal, Angus Beef Bulletin, Angus e-List and Angus Beef Bulletin EXTRA. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.