Implications for Bull Fertility and Productivity
STILLWATER, Okla. (Oct. 9, 2014) — Cow-calf producers weighing the potential advantages of implementing estrus synchronization and artificial insemination (AI) may want to consider the results of a study that evaluated the breeding performance of bulls used for natural service. During the Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium hosted Oct. 8-9 in Stillwater, Okla, University of California–Davis (UC–Davis) extension beef cattle specialist Alison Van Eenennaam provided an overview of the California Commercial Ranch Project. She explained how DNA parentage testing was applied to more than 5,000 calves during a period of three years to evaluate sires for prolificacy and economic return.
Alison Van Eenennaam says when each bull’s contribution to ranch income was evaluated, sire prolificacy was the most significant factor.
According to Van Eenennaam, the participating ranches managed from 700 to 900 cows each, which were divided into breeding groups that were exposed to multiple sires. Breeding season varied by ranch, from 60 days to 120 days. The number of bulls turned into breeding pastures varied from two to nine head, but all ranches maintained a breeding ratio of one bull per 25 cows. Sires were predominantly Angus, but bulls representing several other breeds also were involved. All bulls had passed a breeding soundness examination prior to use.
Van Eenennaam said the results showed a wide variability of individual reproductive performance. The number of progeny per sire ranged from zero to 64 calves per calf crop. On average, about 4% of bulls sired no calves, regardless of breed. Results also showed that the most prolific bulls sired the greatest number of early-born calves, which generally posted the heaviest weaning weights.
When each bull’s contribution to ranch income was evaluated, sire prolificacy was the most significant factor. Bulls siring the most calves returned the most income, but tools for selecting sires for prolificacy remain elusive. Van Eenennaam cited a positive correlation between bull scrotal circumference and prolificacy, but the trait explains only about 12% of variation among bulls.
“Based on the results of this study, the high cost of herd bulls, and the development of reliable and fixed-time AI protocols,” opined Van Eenennaam, “it may be time for commercial producers to re-evaluate the economics of using elite genetics available via AI sires versus the exclusive use of natural-service bulls.”
Van Eenennaam spoke during Thursday’s ARSBC session focused on use of genomics for reproductive improvement. For more information, visit the Newsroom at www.appliedreprostrategies.com to view her PowerPoint, read the proceedings or listen to the presentation.
Comprehensive coverage of the symposium is available online at www.appliedreprostrategies.com. Compiled by the Angus Journal 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 the Angus Journal. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.