The PROC Mixed procedure of SAS v. 9.2 (SAS Inst. Inc., Cary, NC) was used to analyze the data. The effect of dietary treatments (reduced CP vs. standard CP) and different feeding phases (1 to 5) on gas emissions were treated as fixed factors in the mixed model. Pig groups, allocated to different rooms randomly at the start of the Phase 1, were treated as a random factor. Room was nested within dietary treatments. In addition, the same group of pigs was measured multiple times (from Phase 1 through Phase 5), therefore a repeated-measures analysis was applied to the phase factor.