As concerns about air pollution from large dairies and other concentrated animal feeding operations (CAFOs) continue to mount, scientists are reporting a practice that could cut emissions of an exceptionally abundant agricultural gasammoniaby up to 30%.
In the May-June 2011 issue of the Journal of Environmental Quality, a team led by Mark Powell, a soil scientist with the USDA Agricultural Research Service's U.S. Dairy Forage Research Center in Madison, WI, describes how natural plant compounds known as tannins can reduce both the amount of nitrogen cows excrete in urine, and the action of a microbial enzyme in manure that converts the nitrogen into ammonia on the barn floor.
The U.S. EPA already monitors ammonia emissions from large animal operations under the "Superfund" act, and in April a coalition of citizen groups petitioned the agency to begin regulating ammonia under the Clean Air Act, as well. Besides its pungent smell, ammonia that volatilizes from cattle manure is highly reactive in the atmosphere, forming particulates that travel long distances and contribute to environmental problems such as acid rain, nutrient pollution, and smog.
Feeding tannins to cattle could not only help dairy farmers reduce these impacts and meet regulatory standards, Powell says, but tannins could also boost nitrogen use efficiency in cows, thereby decreasing the need for expensive protein supplements. Only 20 to 35% of feed nitrogen ends up in milk on commercial dairy farms, with the remainder excreted about equally in manure and urine as the compound, urea.
Urea is produced when nitrogen-rich proteins break down mainly in the cow rumen, forming ammonia gas that's eventually converted to urea before being excreted. Tannins are thought to cut urea production by somehow allowing more protein to escape digestion in the rumen and enter the cow intestine, where it's used more efficiently to produce milk protein.
|Contact: Sara Uttech|
American Society of Agronomy