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Natural service bulls

Natural-service Bull
Performance and Production

Dan Drake

Bulls with the greatest impact on profitability weren’t the bulls with the highest weaning or yearling weight EPDs, or the ones that sired the heaviest calves, said Dan Drake of UC–Davis. Bulls that sired the most calves had the greatest positive economic impact.

Natural-service breeding remains a dominant management practice among U.S. cow-calf producers — especially in commercial herds. Particularly in western range areas, producers often manage large groups of cows in large multi-sire pastures. Even though a battery of bulls shares the work, producers can determine sires of individual calves through DNA testing. Researchers using parentage testing have found that bulls in a common breeding pasture certainly don’t share the work equally.

As a member of University of California–Davis (UC–Davis) Extension personnel, Dan Drake has been involved with paternity and performance research showing that some bulls are overachievers and others are slackers. Drake shared what research suggests regarding how bulls really affect ranch economics.

According to Drake, the three-year study was based on data collected from more than 5,000 sire-identified calves representing 15 calf crops on three California ranches. Calves came from both spring- and fall-calving herds. Breeding seasons ranged from 60 to 120 days, but all ranches used a 25:1 cow-to-bull ratio in breeding pastures of 100 acres or less.

“The average number of calves sired per bull was 18.9. In every calf crop, some bull distinguished himself by siring over 40 calves. Some bulls sired very few,” said Drake. “One bull actually sired 64 calves in a crop. One bull sired one calf, and more than one bull sired no calves at all.”

Drake said the study revealed some interesting things about the most prolific bulls. For instance, some bulls successfully mated with 10-12 cows per day. It was not uncommon for one-third of a bull’s single-season progeny to have been sired during one 24-hour period. Also, nearly all of the difference in bull prolificacy was represented in the first half of the breeding season. Prolific bulls generated the most conceptions in weeks three, four and five.

Applied reproductive strategies in beef cattle symposiumDrake said the study suggests that varying prolificacy of herd bulls has implications for home-raised replacement females, since most heifers born in the first half of the calving season were daughters of prolific bulls. Selection of early replacement females from prolific sires would be predicted to have a positive effect on herd fertility.

According to Drake, the study illustrates how important reproduction is to profitability, because prolific bulls had the greatest positive impact to the ranches economically.

“It wasn’t the bulls with the highest weaning weight or yearling weight EPDs. It was not the sires of the heaviest calves,” said Drake. “It was the bulls that sired the most calves.”


Editor’s Note: Visit the Newsroom at to listen to Drake's presentation and to view his PowerPoint slides and proceedings paper. This comprehensive coverage of the symposium is compiled by the Angus Journal editorial team. The site is made possible through sponsorship by the Beef Reproduction Task Force.

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