Effects of a reduction of diet crude protein content on gaseous emissions from deep-litter pens for fattening pigs

Two successive batches of 32 fattening pigs per batch were each divided into 2 homogenous groups of 16 pigs fed either a high crude protein (CP) level diet (HP-groups) or a low crude protein level diet balanced with synthetic amino acids (LP-groups). Pigs were raised on straw-based deep litters in separate rooms according to diets. Once a month, the emissions of ammonia (NH3), nitrous oxide (N2O), methane (CH4), carbon dioxide (CO2) and water vapour (H2O) were measured continuously for 6 days consecutively. The mean nitrogen (N) intakes of pigs from HP-groups and LP-groups were 6.83 kg and 5.78 kg per pig respectively with mean initial and final pig body weights of 26.6 and 111.4 kg. There was no significant difference between the daily weight gains with regards to the diet CP content. At the end of the fattening periods, the N-contents of the litters were on average 1.84 kg per pig for the HP-groups and 1.56 kg per pig for the LP-groups. Gaseous emissions in the room with LP-groups were, compared with the emissions in the room with HP-groups, 26.1% lower for NH3 (10.60 vs. 14.35 g per pig per day), 12.8% lower for CH4 (13.12 vs. 15.04 g per pig per day) and 2 times higher for N2O (1.02 vs. 0.52 g per pig per day). The emissions of CO2 and H2O were not significantly different according to the diet CP level.