BioCycle May 2004, Vol. 45, No. 5, p 27
As of January 1, 2004, nonambulatory cattle have been banned from the human food supply. With rendering capacity on the decline, composting has become a viable solution.
In December 2003, USDA Secretary Ann Veneman banned nonambulatory “downer” cattle from the human food supply, creating a challenge with how to manage an estimated 150,000 disabled animals each year. In some cases, these cattle are not diseased, but instead have been injured during birthing or mating. Veneman, wanting to build confidence in the U.S. meat supply after discovery of a downer cow in the Pacific Northwest possibly infected with Mad Cow disease or BSE, instituted the ban. “Sending downer cattle to rendering plants already had become more costly because of the decline in prices and demand for tallow, bone meal and other commodities produced from carcasses,” says Jean Bonhotal, a composting specialist with the Cornell Waste Management Institute (CWMI) in Ithaca, New York.
In addition, growing numbers of rendering plants and slaughterhouses are closing due to tighter restrictions on processing livestock into animal feed. For example, Swanton Packing, the largest slaughterhouse and packing facility serving the New England states, closed recently. “This doesn’t leave dairy farmers with many options to manage downer cattle and mortalities in this region,” says Brian Jerose of Waste Not Resource Solutions based in Enosburg Falls, Vermont. Jerose is collaborating with Bonhotal – and Craig Williams at Penn State University – on a two-year SARE (Sustainable Agriculture Research and Education) grant to conduct outreach, training and education on composting downer cattle mortalities and slaughtering residuals through demonstrations, posters, videos and fact sheets. “When you get into 300 to 500 head dairies with young stock as well, there can be as many as 40 downers/year. Disposing of those animals is becoming a significant cost.”
CWMI and Jerose have been working with farms in New York and Vermont on “natural rendering,” or composting of whole animal carcasses and slaughtering residuals on the farm. They have found that it is economical and environmentally sound for all downer cattle that do not show signs of neurological disease, such as BSE (bovine spongiform encephalopathy). “The heat generated by thermophilic composting – 130° to 160°F – reduces most pathogens in the compost pile,” says Bonhotal.
With rendering options limited – and with the federal ban instituted last December – farmers often resort to burying carcasses in shallow pits or leaving them to decay above ground. “Either of those practices can endanger the health of domestic livestock, wildlife and pets,” notes Bonhotal, “while runoff can contaminate nearby water sources. None of those problems should occur with a properly managed compost operation.” CWMI has a how-to bulletin, “Natural Rendering: Composting Livestock Mortality and Butcher Waste,” on its web site (http://compost.css.cornell.edu/naturalrenderingFS.pdf).
BIOSECURITY ON FARMS
In April, Iowa State University launched a new web site, Emergency Livestock Mortality Composting in Iowa. The site summarizes the objectives, research methods and preliminary results of a three year study (2002-2005) in Iowa of seasonal performance, environmental impacts, and biosecurity of using composting for disposal of cattle and other large animal carcasses. “Iowa is a leader in poultry and livestock production,” explains Tom Glanville, in the Department of Agricultural & Biosystems Engineering at Iowa State. “A disease like the 2001 foot-and-mouth outbreak in Great Britain could require emergency disposal of millions of animals in Iowa. The state’s rendering industry would not have the capacity to handle a widespread outbreak. And the Iowa Department of Natural Resources estimates that as much as 40 percent of Iowa’s land area is poorly suited for mass burial of animals. Further, Iowa does not have a large amount of enclosed high temperature incineration capacity, and open incineration of animal carcasses would produce unacceptable air pollution, as was the case in Great Britain.”
Researchers have been testing a simple composting design that can be constructed quickly in an emergency using on-farm equipment and cover materials. They have been composting cattle carcasses that average 1,000 lbs each. Four carcasses (4,000 lbs total) were put in each test windrow. Piles are built with a 24-inch base layer, a single layer of carcasses, and a sufficient amount of material to cover the carcasses and shed precipitation (minimum cover 18-inches). This typically results in centerline pile heights of approximately 7-feet (approximately half of the base width). Researchers estimate that approximately 12 cubic yards of cover/base material are needed for each 1,000 lb animal. (This is equivalent to one ton of ground hay or straw, 1.4 tons of ground cornstalks or 3.2 tons of corn silage.) Carcasses are placed in a single layer (no stacking) to minimize the potential for leachate release and excessive pile settling. The piles are not turned because it is assumed that in a true livestock disease emergency, cattle carcasses would contain infectious organisms and turning would increase the potential for airborne disease transmission.
Three different materials commonly available at cattle or dairy operations are being tested for covering the carcasses – corn silage, ground cornstalks and dry or moist manure capped with ground straw. To evaluate year round performance, composting test units are constructed at three times of year – hot/dry weather (summer), cold weather (winter) and cool/wet weather (spring). Virus inactivation and virus retention data are collected, using two avian virus strains via placement in the composting test piles.
As of March 2004, 21 test piles containing 42 tons of carcasses have been built. The approximate decay time for 1,000 lb carcasses (unturned) was generally eight to 12 months or less under all weather conditions when using silage, ground cornstalks or hay/manure, report the Iowa researchers. Some trials begun during warm weather have taken less than six months. The three cover materials field tested all appear to achieve complete carcass decay in about the same amount of time. However, test units constructed with corn silage appear to have the best potential for killing pathogens, notes the Iowa State report: “Silage test units typically produce the highest core temperatures in the shortest amount of time following construction of the units. Internal temperatures also tend to be more consistent throughout the pile, and persist longer than in test units constructed with ground cornstalks or hay/manure.” In general, odors were not an issue during the trials.
Preliminary results of field biosecurity tests using two common avian vaccine viruses suggest that composting windrows constructed with the recommended depths of cover material can retain and inactivate viruses within three to four weeks during cold weather, and in a matter of days during warm weather. Nonetheless, Iowa State researchers do not recommend spreading compost from nondiseased cattle on grazing land, or on land used to produce human or animal food crops that will be consumed without further processing. Limited sampling of cattle mortality compost has shown total N content in finished compost of roughly 0.6 to 0.7 percent (wet weight basis) where silage and ground cornstalks have been used as cover material. Total phosphate content for the same composts was in the 0.4 to 0.5 percent range.
The Iowa State research project, “Environmental Impact & Biosecurity of Composting for Emergency Disposal of Livestock Mortalities,” is primarily funded by the Iowa Department of Natural Resources with supplemental funding through the National Research Initiative of the U.S. Department of Agriculture. The project website is: http://www.abe.iastate.edu/cattlecomposting.