, diet formulation based on ideal digestibility of CP and AA (Stein et al., 2007; Moughan and Fuller, 2003)
and the inclusion of synthetic AA (e.g. Canh et al., 1998) into pig diets. Almost half of the N excreted by a growing-finishing
pig via urine and feces can emit during storage ofthe manure in the manure pit and during surface application ofthe manure.
The underlying transformation of urea into NH3 is catalyzed by the enzyme urease that is present in bacteria of the digestive
tract or soil.