SOW BODY COMPOSITION FOR IMPROVED ESTIMATION OF FARM PHOSPHORUS MASS BALANCE

Oil livestock farms, research and government regulations have established that phosphorus (P) accumulated ill the manure is the limiting factor when determining land base requirements for nutrient management plans. Because P is a stable element, the total P accumulated in manure may be determined by mass balance. In this study total body P content Of cull sows was chemically determined in order to facilitate more accurate P mass balance calculations for swine breeding herd farms. Fifteen sows were removed from a central Michigan swine breeding herd, following normal farm culling protocol, and slaughtered. Each sows blood, viscera including digesta and carcass were individually processed and sampled such that each sows individual components and each sow's total body content for protein, fat, ash, and nine minerals, including P were analyzed. Average P content of the 15 cull sows was 0.563% P. A P mass balance model for an example 2,400-sow case farm using this value for cull sows, and those reported in the literature for other specific stages of production it the time when animals enter or del)art the farm, were used to estimate annual accumulation P2O5 in manure. Die P mass balance model using stage-specific, chemically-determined values, estimated there would be 29,751-kg manure P2O5 accumulated annually by this farm, 9% to 31% greater than other estimates made using currently available methods. A nutrient management plan developed using a mass balance model with stage-specific, chemically-determined total or whole body P requires a larger land base, bill that estimation reduces the risks of P accumulating in the soil and future restrictions oil the use of that land for manure applications because of high soil P levels.