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In recent years, costs of animal mortality pick-up have increased substantially due to reduction in demand for rendered products. Carcass disposal by burial has been the most common method while incineration of poultry and swine carcasses is also practiced in several states. These methods raise concerns over groundwater contamination at burial sites, and odor, air pollution, and unsuitability of disposing large carcasses by incineration. As the cost of dealing with mortalities and environmental concerns increase, the animal feeding operations (AFO) use and/or acceptance of on-farm mortality composting could very easily make it a preferred method of handling livestock losses. This paper presents results of a large- carcass (horse and cow mortalities) composting study using an in-bin, static pile composting system. Bins were created using large hay bales and spent horse bedding was used as a co-composting material. In one case, the carcass compost piles were turned at 3 and 6-month intervals after the start of composting. In the other case, the compost piles were built by placing the carcass above wooden pallets and turning the pile only once in a 6-month period. This was a low maintenance composting system because no pre processing of mortalities (cleaving, grinding etc.) was performed, no extra moisture other than that from the natural precipitation was added to the compost pile, and piles were turned no more than twice during the nine-month trial period. Within a few days after composting began, all piles achieved temperatures above 55 OC and remained at or above this temperature for several days or weeks. Turning piles without the wooden pallets after 3 months of composting resulted in a much greater temperature increase for the larger carcass (cow carcass weighing 909 Kg) than that for the smaller (horse carcass weighing 500 Kg) carcass. After six months of composting with and without the wooden pallets, similar carcass conditions in terms of faint odors and a high degree of large bone biodegradation were observed. After 9 months of composting, the C:N ratios of all compost piles were nearly one half of the horse bedding used as a co-composting material. Pathogenic evaluation of 9-month old carcass compost piles indicated low counts of salmonella and fecal coliform bacteria. The final product was ready to be land applied without the need to screen out large bones as they shattered and disintegrated easily. Based upon these results and observations, it was concluded that an in-bin, low maintenance carcass and horse bedding composting operation for the disposal of cow and horse mortalities can be carried out successfully in temperate climates during seasons of normal precipitation.