The biosecurity of composting as an emergency disposal method for cattle mortalities caused by disease was evaluated by conducting full-scale field trials begun during three different seasons and using three different envelope materials. Process biosecurity was significantly affected by the envelope material used to construct the composting matrix. Internal temperatures met USEPA Class A time/temperature criteria for pathogen reduction in 89%, 67%, and 22%, respectively of seasonal test units constructed with corn silage, straw/manure, or ground cornstalks. In trials begun in the winter, survival times of vaccine strains of avian encephalomyelitis and Newcastle disease virus were noticeably shorter in silage test units than in the other two materials, but during summer/spring trials survival times in ground cornstalk and straw/manure test units were similar to those in test units constructed with silage.