The effect of feeding reduced crude protein (CP) diets on air emissions was evaluated using barrows fed over the
course of four feeding phases: G1 (beginning at 24.5 kg BW), G2 (55.3 kg), F1 (87.2 kg), and F2 (111.4 kg). Pigs were offered a control diet (C), a low CP diet (LCP) or an ultra low CP diet (ULCP). Both the LCP and ULCP diets were supplemented with crystalline amino acids to avoid performance loss. It was found that diet had no effect on mass of manure produced; however TKN and NH3-N concentration decreased with decreasing diet CP (79, 67, 57 g kg-1 and 54, 44, and 35 g kg-1, respectively, for C, LCP, and ULCP diets).