Nitrogen (N) losses from four high-rise laying hen houses, representing four commercial layer farms in Iowa, were determined from measured performance data of Hy-Line W-36 White Leghorn layers (i.e., manure production, egg production, feed intake, body weight, and mortality). Nitrogen loss was 25, 33, 37, and 41% for Farms A, B, C, and D, respectively, based on the Total Kjeldahl Nitrogen (TKN) in feed. A significant factor contributing to the difference in the N losses was the moisture content (MC, percent on an as-is basis) in manure stored in the ventilated manure storage area of the layer houses. The higher the MC, the higher the ratio of NH 3 /TKN Manure in the stored manure, and therefore, the higher the percentage of N loss. Mathematical relationships were developed. Manure handling systems played an important role in N loss by influencing MC of the manure which, in turn, affects rate of manure decomposition. Understanding the factors affecting decomposition and N loss mechanisms of layer manure could provide a means to significantly reduce ammonia emissions to the atmosphere from poultry facilities.