Composting is a process causing important nitrogen losses (from 46,8% to 77,4% of the initial total N). Losses also occur under the form of NOx to the air (<5%) and also as leachates (9,6 to 19,6% of the initial total N). Composting of animal wastes is not an efficient process if we consider it under a fertilizer source and also if we consider the environmental impact resulting from it (emissions, leaching).