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Abstract  Genetically modified pigs have been developed that are able to use phosphorus (P) in the feed more efficiently and thereby reduce the amount of P excreted in the manure. Improved digestibility would also change the chemical composition of the manure. The objective of this study was to determine how improved P digestibility affects the manure composition and the associated carbon dioxide (CO2) emissions and nitrogen (N) loss through denitrification when the manure is applied to soil. Aerobic and anaerobic incubation studies were conducted to evaluate CO2 emissions and denitrification losses from two soils (Brookston clay loam and Harrow sandy loam) amended with pig slurry (115 mg N kg−1 soil) from transgenic pigs as well as from conventional pigs. In addition, both the transgenic and conventional pigs were fed either a low-P diet or a conventional P diet, and the effects of diet type on CO2 emissions and denitrification losses were examined. Carbon dioxide emissions were 17% lower (P P 2 emissions nor N loss through denitrification were affected by pig genotype when the manure was added to the sandy loam soil. The diet type (conventional P diet or low-P diet) did not affect either CO2 emissions or N losses through denitrification in either the Brookston clay loam or Harrow sandy loam soils. [ABSTRACT FROM AUTHOR]

Abstract  Genetically modified pigs have been developed to enable them to use phosphorus (P) in the feed more efficiently and thereby reduce the amount of P excreted in the manure. However, there is no information available about how improved P digestibility affects nitrogen (N) and carbon contents in the pig manure and the subsequent dynamics that occur when the manure is applied to soil. An 8-week incubation study was conducted to determine the changes in inorganic N contents of two soils (a clay loam and a sandy loam) treated with pig manure (115 mg N kg−1 soil) from these transgenic pigs as well as from conventional pigs. In addition, both the transgenic and conventional pigs were fed either a low-P diet or a conventional P diet and the effects of diet type on N contents in the manure and the subsequent soil dynamics were examined. There was no difference in total manure N content between transgenic and conventional pigs. However, the ammonium content was lower and the soluble carbon level was greater in manure produced by transgenic pigs than by conventional pigs. The manure excreted by pigs fed with low-P diet contained more total N and ammonium N than the manure from pigs fed with conventional-P diet. Ammonium-N was nitrified completely in the first week of incubation in manure-amended clay loam, while the nitrification process took 4 weeks to complete in manure-amended sandy loam soil. Manure from transgenic pigs not only contained less inorganic N but this N was more rapidly immobilized and/or denitrified compared to the inorganic N produced by conventional pigs. [ABSTRACT FROM AUTHOR]