"That's one of nature's wonders," Hristov said.
Yet the by-products of the animal's digestive system also are among nature's problems, both in the air and in impaired water bodies such as the Chesapeake Bay. Hristov, Lee, and their colleagues are experimenting with sophisticated diets to reduce harmful pollutants that emerge from, ahem, both ends of the cow.
The stakes are high. The U.S. Environmental Protection Agency has proposed mandatory reductions in pollution from Pennsylvania and the five other states in the bay's watershed, each of which is in the midst of determining where the cuts will be made.
Agriculture is a prime target. It accounts for a large share of pollution, in the forms of nitrogen, phosphorus, and sediment. Livestock manure is loaded with nitrogen, which is useful as fertilizer but is an environmental threat when it washes into waterways. Along with phosphorus, nitrogen fosters the growth of excess algae, eventually robbing the water of oxygen.
Some farmers have reduced this runoff pollution by planting vegetative buffers and erecting fences to keep cattle away from streams. Yet of the 250 million pounds of nitrogen that pollute the Chesapeake watershed each year, farms still account for more than 100 million pounds, according to EPA estimates - more than 40 percent of the total.
Enter the scientists.
Cows consume nitrogen in the form of protein in their feed. Some of it is used to produce milk. More than half is excreted as waste.
The Penn State scientists asked: Could they reduce the amount of protein in the diet - and thus the amount of nitrogen in the cow's manure - without affecting milk production?
So far, the answer seems to be yes.
Hristov and his colleagues are conducting several experiments, funded by a $226,000 grant from the U.S. Department of Agriculture.
