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Abstract. Manure collected from open lot animal housing systems experiences significantly greater variability than expected compared to roofed housing systems. Variations in weather conditions, mixing of manure and soil, and variability in operator management of cattle and pens produces substantial variability in manure characteristics and quantity. A large data set collected over a 15 year period from 444 independent pens of cattle feeding (including independent measures nutrient flows and manure collection) provides a highly unique insight to the degree of variability observed and some of the factors influencing this variability within open lot systems. The results of this review suggest significant concern about the use of standard methods for estimating manure characteristics as published by ASABE, NRCS, and MWPS for manure management planning. The analysis also demonstrates the impact of winter vs. summer feeding periods and feed nutrient concentrations on manure characteristics. Finally, the analysis documents the nitrogen balance for winter and summer feeding periods. For the nitrogen fed to beef cattle in the observed Nebraska feedlot, nitrogen exits the feedlot in the following forms and proportions for the summer and winter feeding periods, respectively: 13 and 13% as retained by the animal, 21 and 40% as harvested manure, 63 and 41% as losses (assumed to be primarily ammonia volatilization), and 3 and 3% as runoff.