Farmers caught in the middle -- between the recent federal ban against "downer" animals in the human food chain, as ordered by the United Stated Department of Agriculture (USDA), and rising costs for disposing of cattle that can't walk to slaughter -- now have a practical and economical alternative, according to waste-management experts at Cornell University.

Natural rendering, also known as composting of whole animal carcasses on the farm, is economical and environmentally sound for all downer cattle that do not show signs of neurological disease, such as bovine spongiform encephalopathy (BSE, or mad cow disease), say compost researchers who tested the technique at the Cornell Waste Management Institute.

"The heat generated by thermophilic composting, 130 --160 degrees Fahrenheit, reduces most pathogens entering the compost pile," says Jean Bonhotal, the Waste Management Institute researcher who studied natural rendering and produced a set of printed and videotaped instructions. "But we doubt that composting destroys the prions associated with mad cow disease, so we emphasize this important exception: Animals showing signs of neurological disease must be reported to authorities and disposed of in the manner they recommend."

Otherwise, livestock that are composted with the approved technique -- placed on a bed of wood chips and completely covered with high-carbon material such as sawdust or silage and more wood chips -- are reduced to clean bones in four to six months and to a usable soil amendment in a year. The same technique works with butcher "residuals," the 60 percent of slaughtered livestock that is not salable meat, according to Bonhotal.

"Most people don't realize that composting is a legal and acceptable way of disposing of these materials," Bonhotal says. "Composting of dead livestock can be accomplished in compliance with environmental regulations in most states," she adds, offering an example to make farmers' problems seem trivial: A 30,000-pound right whale that died off the coast of New Jersey was obtained by a museum, trucked to Ithaca and covered with horse manure. After 12 months the compost pile was opened by museum workers, who separated bones from composted soil and assembled the whale skeleton for display at the Paleontological Research Institution's Museum of the Earth.

"If natural rendering works on a 15-ton whale, it won't have a problem with a 1,200 pound steer," Bonhotal says.

Even before the Dec. 30, 2003, order by USDA Secretary Ann M. Veneman banning downer cattle from the human food supply, dealing with the estimated 150,000 disabled animals a year in the United States was becoming problematic, Bonhotal notes. Sending downer cattle to rendering plants had become more costly because of declines in price and demand for hides, tallow, bone meal and other commodities produced from carcasses.

Some rendering plants closed altogether and others hiked the fees to pick up carcasses from farms, while more farmers resorted to burying carcasses in shallow pits or leaving them to decay above ground. Either of those disposal practices can endanger the health of domestic livestock, wildlife and pets, Bonhotal observes, while run-off can contaminate nearby water sources.

None of those problems should occur with a properly managed compost operation, the Cornell expert says. The finished compost can either be used as a base for the next cycle of natural rendering or can be used as a soil amendment for hay, field corn, winter wheat or tree plantations. Although it is particularly rich in the plant nutrients nitrogen (N), phosphorus (P) and potassium (K), compost from animal carcasses should not be used to fertilize crops that will be consumed by people, the Waste Management Institute recommends.

For more information, the bulletin "Natural Rendering: Composting Livestock Mortality and Butcher Waste" is available at the Web site http://compost.css.cornell.edu/naturalrenderingFS.pdf or by contacting the Cornell Waste Management Institute, Rice Hall, Cornell University, Ithaca, N.Y. 14853. E-mail cwmi@cornell.edu . A 20-minute award-winning video by the same title, produced by Insights International, also is available from the institute.