A project conducted by a team of researchers in Pennsylvania State University’s College of Agricultural Sciences is investigating whether feeding cattle low-protein diets might result in the animals more efficiently utilizing dietary nitrogen, which may in turn reduce ammonia emissions from dairy operations.

"There is sufficient evidence that low-nitrogen feeding and management practices are the most effective method for reducing nitrogen and ammonia emissions from animal-feeding operations," says Alexander Hristov, associate professor of dairy nutrition at Penn State and lead investigator for the project. "These practices can result in potential cost savings to the producer and a drastic reduction in nitrogen imports and gaseous nitrogen emissions from the farm."

According to Hristov, the overall objective of the project is to demonstrate that dairy cows and heifers can be managed on low-crude-protein diets without affecting productivity or animal health. The strategy will result in a significant reduction in whole-farm nitrogen imports, nitrogen losses and ammonia volatilization from manure, and will increase farm profitability through increased "income over feed cost," he explains.

Funded by a $226,000 special grant for improved dairy management practices awarded by the U.S. Department of Agriculture this year, the research is especially important in Pennsylvania, where one of the critical water-quality issues is the discharge of nutrients into the Potomac and Susquehanna River watersheds, which feed the Chesapeake Bay.

"The environmental management of these two watersheds is imperative for restoring the ecological health of the bay," Hristov, says. "As animal farms are the biggest nonpoint sources of nitrogen discharges to the Chesapeake Bay, reducing nitrogen losses from animal-feeding operations in the bay area is essential for improving the environmental health of the ecosystem."

The Penn State project is designed to test how synthetic, ruminally protected essential amino acids, which are known to limit milk production, influence yields of milk and milk protein in high-producing dairy cows fed protein-deficient diets. The working hypotheses for the lactating dairy cow part of the project is that low-crude-protein, metabolizable-protein-deficient diets need to be supplemented with these essential amino acids to maintain high milk production. The project also will generate valuable information on the potential for reducing nitrogen losses and ammonia emissions from dairy manure by decreasing dietary protein concentration.

The researchers hope study results can be used to more accurately determine amino acid requirements of cows fed diets with varying protein content and in early stage of lactation, when most likely to respond to supplemental amino acids, Hristov notes.

"The heifer experiment will test our hypothesis that efficiency of dietary nitrogen utilization can be significantly increased and nitrogen losses reduced if rumen fermentation is optimized, thus minimizing potential negative metabolic consequences of limited feeding of dairy heifers," he says.