A two-year project was begun in Iowa in 2002 to test the decay performance, air and water environmental impacts, and bio-security of using composting for emergency disposal of cattle carcasses in the event of a foot-and-mouth disease outbreak. Of the three emergency cover materials tested to date, silage produced the highest and most sustained internal heat, the most rapid and thorough carcass decomposition, and the most rapid destruction of avian vaccine viruses introduced into the piles for bio-security testing. Although internal temperatures within ground cornstalk cover material were much lower than in the silage, carcass decomposition appeared to occur almost as rapidly as in the silage. The cornstalk material produced more collectable leachate with higher pollutant concentrations than the silage. Downwind odor from test units constructed with ground cornstalk, which has a much higher air permeability coefficient than silage, appeared to be strongest and more frequent during the initial 2–3 weeks following construction of the piles.