Begin preweaning to manage bull development to optimize fertility.
SIOUX FALLS, S.D. (Dec. 3, 2012) — Management of nutrition during development of breeding bulls can be a controversial topic. Nearly all discussion is focused on management of bull calves after they are weaned. According to Albert Barth, veterinarian and professor at the University of Saskatchewan’s Western College of Veterinary Medicine, nearly all bull development research also has concentrated on the postweaning period. He thinks researchers have overlooked a very important period of development in a bull's lifetime — calfhood.
"I suspect it makes a bigger difference than variations in postweaning nutrition," said Barth in a presentation delivered at the Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium Dec. 3-4, in Sioux Falls, S.D. "There are indications of a strong effect of calfhood nutrition and health on age at puberty and testis size, implying earlier maturity and larger lifetime testis size."
Barth said there are limited data explaining the effects of calfhood nutrition. Still, evidence suggests smaller scrotal circumference in yearling bulls raised by first-calf heifers (compared to bulls raised by older dams) may be due to lower milk production of their mothers, fetal programming effects or both. Barth explained how calfhood nutrition affects pituitary gland secretion of gonadotropin hormone. Bull calves experiencing lower gonadotropin secretion are likely destined to mature later and exhibit smaller testes. Studies confirmed that superior calfhood nutrition resulted in higher gonadotropin secretion, resulting in larger testes at a year of age and earlier onset of sperm production.
"It's likely that final testes size is determined before weaning," stated Barth, recommending that management strategies to optimize bull fertility should focus on the time bull calves are still nursing the cow. "Nutrition throughout calfhood and the postweaning period affects age of puberty, but you can’t compensate for restricted energy during calfhood.”
Barth urged attention to developing practical health and nutrition programs for young bulls, suggesting an ideal nutrition program should be based on breed and frame size. He recommended a program of moderate cost, allowing for growth at 2.5 pounds (lb.) to 3.0 lb. of gain per day, but avoiding excessive body condition. High-energy diets fed postweaning may result in larger scrotal circumference at a year of age, but part of the increased size is probably due to scrotal fat.
Barth spoke during Monday's ARSBC session focused on inseminator efficiency and male fertility. Visit the Newsroom at www.appliedreprostrategies.com to listen to his presentation and to view the accompanying PowerPoint slides and proceedings paper.
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 Reproductive Task Force and LiveAuctions.tv.
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.