Virginia Tech researchers in the Department of Dairy Science in the College of Agriculture and Life Sciences are using a grant from the U.S. Department of Agriculture's Natural Resource Conservation Service (NRCS) to offer incentive payments to dairy farmers who reduce phosphorus overfeeding on their farms. This outreach program follows almost a decade of research on the dietary nutrient management of dairy cattle in Virginia.

“So far, we have registered 183 dairy farms in Virginia to monitor phosphorus intake,” said Katherine Knowlton, associate professor of dairy science and project director. “Dairy farmers who are enrolled in this scaled incentive program can receive payments of up to $12 per milking cow per year for reducing phosphorus in their dietary feed.”

Totaling more than $1.7 million, the research funding can cover more than 200 eligible dairy farmers. Producers must feed their dairy cattle less than 15 percent excess phosphorus to be eligible for an incentive payment at the end of the year. Other researchers involved in this project are Charlie Stallings, professor in the Department of Dairy Science and specialist for Virginia Cooperative Extension; Bob James, professor in the Department of Dairy Science; Mark Hanigan, associate professor in the Department of Dairy Science; and Rick Kohn, associate professor at the University of Maryland’s Department of Animal and Avian Sciences.

Through their research on dietary nutrition management and precision phosphorus feeding on Virginia dairy farms, this team has shown that overfeeding phosphorus not only pollutes the environment but also does not benefit the livestock.

“Every extra gram of phosphorus fed to an animal is excreted,” Knowlton explained. “Unlike dietary energy, phosphorus is not stored in the body for later use.”

Researchers have also debunked a longstanding belief in a high phosphorus requirement for reproduction in dairy cattle. “We often feed early lactation cows nutrients they need specifically for this life stage, but for phosphorus there is no point,” said Knowlton, who noted that early lactation cows still pull phosphorus and other nutrients from their bones even when fed phosphorus in excess. “We are overfeeding dairy cattle with phosphorus, and they aren’t using the excess nutrients.”

Phosphorus pollution from the livestock industry can trigger eutrophication, an overgrowth of algae in surface water that accelerates the biological death of an aquatic system. Because aquatic plants require significantly less phosphorus to grow than terrestrial plants, an overabundance of phosphorus prompts phytoplankton, or algae, to propagate at a rapid pace. Known as an algal bloom, this phenomenon depletes the amount of dissolved oxygen in surface water, leading to fish kills. When this happens, algae populations are often so dense that they prevent an adequate amount of sunlight from reaching submerged aquatic vegetation such as sea grasses, which shelter aquatic animals.

Without intervention, this process will continue until all of the marine life in a lake or bay vanishes from lack of oxygen. Scientists have attributed “dead zones,” or giant, lifeless portions of a body of water, to excess phosphorus and other nutrients. National Geographic reports that a “dead zone” in the Gulf of Mexico spans more than 8,000 square miles at its peak, an area almost the size of New Jersey.

“Virginia’s livestock industry is concentrated in the Chesapeake Bay Watershed,” Knowlton said. “We have about 70,000 dairy cows and a significant poultry industry in this area.”

This project forms the core of the Department of Dairy Science’s “Targeted Environmental Solutions for Virginia’s Dairy Farms” education and outreach effort. A previous article explains the origin, funding, and additional aspects of the project.

About the College of Agriculture and Life Sciences

Nationally ranked among the top research institutions of its kind, Virginia Tech’s College of Agriculture and Life Sciences focuses on the science and business of living systems through learning, discovery, and engagement. The college’s comprehensive curriculum gives more than 2,200 students in a dozen academic departments a balanced education that ranges from food and fiber production to economics to human health. Students learn from the world’s leading agricultural scientists, who bring the latest science and technology into the classroom.