Effect of reduced crude protein on ammonia, methane, and chemical odorants emitted from pig houses

The aim of the present study was to investigate the effect of reduced crude protein level in finisher diets on ammonia, methane, and chemical odorants emitted from pig houses. Over a period of 44 days, pigs in two similar houses with 32 pigs (55-100 kg) in each were fed either a low-protein or a standard protein diet containing 136 or 159 g crude protein kg−1, respectively. The diets were formulated to be isoenergetic (8.1 MJ net energy kg−1 as fed) and were supplemented with indispensable amino acids to fulfill amino acid recommendations. A photoacoustic gas monitor was used to measure ammonia and methane during the whole experimental period, and Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) was used to measure chemical odorants during the last 11 days. The results demonstrated that the crude protein level could be reduced by supplementing indispensable amino acids without impairing growth, feed utilization, and meat percentage. Reduced crude protein level lowered the ammonia emission, whereas no significant effect was seen on the methane emission and the total odor activity value based on chemical odorants. In conclusion, reduced crude protein level is an effective method to reduce ammonia emitted from pig houses. However, more research is needed to investigate how optimization of the amino acids content can influence the emission of individual chemical odorants. Furthermore, PTR-MS was demonstrated to be a suitable method for estimating the effect of a given feeding strategy on the emission of chemical odorants.