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Angus Journal
Copyright © 2015
Angus Journal

Bull Management for
Optimal Reproductive Performance

JOPLIN, Mo. (Sept. 1, 2011) — Speaking during the Applied Reproductive Strategies in Beef Cattle (ARSBC) conference in Joplin Aug. 31-Sept. 1, University of Missouri (MU) veterinarian Dietrich Volkmann discussed commonsense practices for managing breeding bulls. To a fairly familiar list of recommendations he added a warning related to external parasite treatments involving a common class of insecticides. Volkmann cited evidence suggesting pyrethroid products may affect bull fertility.

Numerous commercially available treatments for flies and other external parasites, including sprays, pour-ons and insecticide-impregnated ear tags, utilize pyrethroid formulations. According to Volkmann pyrethroid sprays and pour-on products have been implicated in the development of severe secondary sperm defects and poor sperm motility among breeding bulls exposed to the products.

Dietrich VolkmannFor herds in which trichomoniasis has been diagnosed and carrier bulls eliminated, Veterinarian Dietrich Volkmann advised producers to think about buying expendable bulls as replacements, at least for the short term.

Research indicates pyrethroids may inhibit production of an enzyme responsible for the conversion of testosterone to dihydrotestosterone, a hormone necessary to the proper function of multiple accessory sex glands. As a result, said Volkmann, bulls may produce lower volumes of semen, sperm cells may be abnormal and the ‘freezeability’ of sperm collected from artificial insemination (AI) sires may be compromised. It is a temporary effect; semen quality will improve in four to six weeks.

“All evidence is case-based, meaning there is no controlled research,” Volkmann stated, “but I advise producers to stay away from pyrethroids for six to eight weeks before the onset of breeding season.”

Beyond that warning, Volkmann advised producers to apply the usual litany of good management guidelines, starting with selecting bulls that are appropriate for desired goals. For example, when selecting a bull to breed heifers, calving ease may be the most important trait. Volkmann also advised against selecting bulls fresh from a confined feeding situation for immediate use for pasture breeding. Such bulls may need time to adapt to a diet of grazed forage. Furthermore, Volkmann said bulls that are obese and have not experienced sufficient exercise in recent months are more subject to musculo-skeletal injuries during breeding.

Volkmann advised producers to consider a bull’s age and experience when determining a bull-to-cow breeding ratio. He also recommended that bulls used in multiple-sire pastures be of similar age. Young and smaller bulls may not compete successfully against older and heavier bulls.

Recommending annual vaccination against clostridial and respiratory diseases, bovine viral diarrhea (BVD), and Campylobacter (vibrio), Volkmann said vaccinations should be administered at least eight weeks prior to breeding season. Every bull, he advised, should receive a full breeding soundness examination four to eight weeks prior to breeding. After turnout in breeding pastures, bulls should be monitored for health and physical well-being, and to determine whether each bull is actively pursuing and servicing females.

For herds in which trichomoniasis has been diagnosed and carrier bulls eliminated, Volkmann advised producers to think about buying inexpensive bulls as replacements, at least for the short term.

“You might want to consider ‘cheap,' and by that I mean expendable bulls, until you are sure the herd is clean,” said Volkmann. “In that situation achieving a high pregnancy rate may be more important than pursuing the specific genetics you want.”

Volkmann spoke during Thursday's ARSBC session focused on reproductive considerations related to the male. Visit the Newsroom at to view the PowerPoint slides and proceedings paper submitted by Volkmann 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.