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Protein’s Effect on Reproduction

Research indicates differences in excess protein in dairy and beef cattle reproduction.

DES MOINES, Iowa (Sept. 7, 2016) — Nutrition and reproduction go hand in hand. It has been documented that excess protein results in a negative relationship in fertility in dairy cattle due to increased concentrations of plasma urea nitrogen and milk urea nitrogen being associated with suppressed fertility. Patrick Gunn, assistant professor and beef cow-calf extension specialist from Iowa State University, explained how protein affects the beef cow’s fertility to attendees of the 2016 Applied Reproductive Strategies in Beef Cattle symposium in Des Moines, Iowa, Sept. 7-8.

Patrick Gunn, assistant professor and beef cow-calf extension specialist from Iowa State University, explained how protein affects the beef cow’s fertility.

He highlighted the relationship of nutrition and fertility in beef cattle, saying that protein is a key nutrient that may be overlooked in rations, especially when cows are grazing low-quality forages. Dietary crude protein is broken into rumen degradable and rumen undegradable protein. He explained that degradable proteins are those that can be absorbed as amino acids for microbial protein synthesis. Undegradable protein is that which is left over and passes to the intestine.

Essentially, the goal of protein supplementation is to supply rumen degradable protein to feed the rumen’s microbial population to support production. While the Nutrient Requirements of Beef Cattle (NRC) was recently updated, he said protein requirements for reproduction have not been fully characterized and the impacts of excess supplementation on reproduction have not been established in beef cows.

While data showed a poor relationship between dietary protein and fertility in dairy cattle, beef cattle research does not support the dairy data. Blood urea nitrogen concentrations don’t appear to be linked to fertility at all in beef cattle. He suggested that the relationship in dairy cattle has to do with metabolic stressors and negative energy balances during peak lactation, which are often during breeding season.

“When metabolizable energy is not a limiting factor, excess dietary protein does not negatively impact reproductive processes and fertility in beef cattle,” he explained, adding that more research should be conducted.

Gunn spoke during Wednesday’s ARSBC session focused on the nutritional effects on reproduction. Visit the Newsroom at, which features comprehensive coverage of the symposium, to view his PowerPoint, read the proceedings or listen to the presentation. Compiled by the Angus Media 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 Angus Media. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.