Scientists say nutrient management in cattle may benefit the environment


UNIVERSITY PARK, Pa. — A project conducted by a team of researchers in Penn State’s College of Agricultural Sciences is investigating whether feeding cattle low-protein diets might result in the animals more efficiently utilizing nitrogen in their diet and reduce ammonia emissions from dairy operations.

Funded by a $226,000 special grant for improved dairy management practices awarded by the USDA 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.


Nitrogen contamination of ground and surface water and air pollution caused by leaching, runoff and gaseous nitrogen emissions from animal-feeding operations are the most important environmental concerns related to animal agriculture, which is known to be the leading polluter of the bay.

“The environmental management of these two watersheds is imperative for restoring the ecological health of the bay,” said Alexander Hristov, associate professor of dairy nutrition and lead investigator for the project.

“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, including Pennsylvania, is essential for improving the environmental health of the ecosystem.”


Following recent efforts by the U.S. Environmental Protection Agency to regulate ammonia emissions from livestock operations, it becomes increasingly important for dairy producers to reduce manure nitrogen excretions and manage their operations in an environmentally responsible manner, Hristov pointed out.

“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,” Hristov said. “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.”

The point

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 explained.

“This 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,” Hristov said.

“Our 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 that 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 noted.

“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 said.


The project includes four experiments with animals from Penn State’s dairy herd. The first involves 36 lactating cows (three groups of 12 cows); experiment two is a production trial with 120 cows (six pens with 20 cows per pen); experiment three is a metabolism trial with eight lactating cows; and experiment four is a metabolism trial with eight heifers.

Also participating in the project from the university’s Department of Dairy and Animal Science are Jud Heinrichs, professor of dairy and animal science, Gabriella Varga, distinguished professor of animal science and Virginia Ishler, manager of Penn State’s dairy complex.


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