In general,the N excretion of pigs can be divided in an inevitable part that occurs due to normal turnover processes of protein
in the animals (Tamminga, 2003), and another evitable part that occurs due to overconsumption of crude protein (CP) or
consumption of unbalanced ratios of amino acids (AA) in the diet (Aarnink and Verstegen, 2007; Rademacher, 2000). Hence,
strategies to reduce environmental impact of animal husbandry include reduction of N supply via feed by phase feeding
(Rademacher, 2000)