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Estimation of nutrient excretion is an essential component in the development of a comprehensive nutrient management plan. Current estimates of nutrient excretion by various classes of swine are outdated and do not allow for prediction of nutrient excretion based on dietary nutrient intake or retention. Thus, our intentions were to develop models for prediction of nutrient excretion based on differing nutritional schemes. The basic approach was a mass balance that calculates nutrient excretion as the difference in nutrient intake (nutrient content and feed intake; NRC, 1998) and nutrient retention (production level, lean growth potential, etc). Estimates of nitrogen, phosphorus, and dry matter excretion were developed for the weanling pig (5 to 20 kg), the growing-finishing pig (20 to 120 kg), and the gestating and lactating sow. For the weanling and growing-finishing pig, intake of nitrogen and phosphorus were estimated based on feed intake and the dietary concentration of the nutrient needed to support a specific fat-free lean tissue gain. Nutrient retention was estimated based on a specific fat-free lean gain. A similar approach was taken to estimate nutrient intake and retention by the sow with the exception that nutrient retention associated with the litter and(or) placenta were estimated. Our estimates of excretion are 14.2, 39.3, 28.8, and 85 g of nitrogen/d and 2.3, 6.7, 9.0, and 21.3 g of phosphorus/d for weanling, growing-finishing, gestation, and lactation phases, respectively. These estimates of nitrogen excretion are greater than current MWPS and NRCS estimates for the weanling pig. The estimate of nitrogen excretion by the growing-finishing pig is greater than these other estimates, but phosphorus is lower. Our estimates for the gestating and lactating sow are quite similar to estimates provided by MWPS and NRCS. The models predict changes in nutrient excretion via dietary manipulation accurately based on published data. Due to the lack of information concerning nutrient excretion under commercial conditions, comparison of the results reported herein to that obtained on commercial farms is difficult. However, based upon the methodology utilized, nutrient excretion can be predicted based upon feed intake, nutrient content of the diet, and production level for pigs managed under commercial conditions.