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Three successive batches of fattening pigs were raised on a deep litter of straw in one room and of sawdust in another. The quantities of litter used per pig were 40 kg of straw and 81 kg of sawdust.Once a month, the emissions of ammonia, nitrous oxide, methane, carbon dioxide and water vapour were measured continuously for 6 days consecutively.Gaseous emissions from pig raising on sawdust-based litter and straw-based litter were respectively 12·16 and 13·61 g per pig per day for ammonia (NH3), 4·96 and 7·39 g per pig per day for methane (CH4), 2·09 and 0·03 g per pig per day for nitrous oxide (N2O), 3·15 and 2·74 kg per pig per day for water (H2O) and 1·32 and 1·30 kg per pig per day for carbon dioxide (CO2). Differences between the emissions of the two litters were significant for N2O and H2O (P 0·01).The nitrogen content of the manures collected at the end of the experiment was 1·47 kg per pig for the straw-based litter and 1·07 kg per pig for that based on sawdust. Nitrogen emissions were calculated under the assumption that no gases volatilized from the litter or from the animals other than NH3 and N2O. With the two litters, about 50% of nitrogen excreted by the pigs was emitted into the atmosphere in the form of N2.

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The aim of this study was to compare the environmental impact of the straw-flow system for fattening pigs with the slattedfloor system by measuring pollutant gas emissions such as ammonia (NH 3 ), nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ), manure nitrogen (N) content and emissions of water vapour (H 2 O). Three successive batches of 32 pigs were fattened. For each batch, pigs were allotted to two groups raised in separated rooms fitted either with a concrete totally slatted-floor system (0.75 m 2 per pig) or with a straw-flow system (0.79 m 2 per pig). With this last system, pigs were kept on a sloped floor, straw being provided daily at the top of the pen. Throughout the fattening period, about 34.4 kg of straw were supplied per pig. The straw, mixed with dung, travelled down the slope by pig motion and went out of the pen to a scraped passage. The solid fraction was scraped every day, stored in a heap in the room and removed every month, 1 week before each period of gaseous emission measurement. The liquid fraction was automatically pumped from the scraped passage into a hermetic tank, which was emptied at the end of each fattening period. Rooms were ventilated mechanically in order to maintain a constant ambient temperature. Once a month, the emissions of NH 3 , N 2 O, CH 4 , CO 2 and H 2 O were measured hourly for 6 consecutive days via infrared photoacoustic detection. Mean daily emissions per pig fattened on the slatted floor or on the sloped floor were, respectively, 4.98 and 13.31 g NH 3 , 0.67 and 0.68 g N 2 O, 15.2 and 8.88 g CH 4 , 548 g and 406 g CO 2 equivalents, 1.61 and 1.77 kg CO 2 and 2.33 and 2.95 kg H 2 O. Except for N 2 O emissions, all the differences were statistically significant (P , 0.001). From the slatted-floor system, the amount of slurry removed per fattening period was on average 256 kg per pig. From the straw-flow system, solid manure amounted on average to 209 kg per pig and liquid manure to 53 kg per pig. The total N-content of the manure was 2.23 kg N per pig with the straw-flow system (solid and liquid manure) v. 3.26 kg N per pig for slurry from the slatted-floor system. This reduction of 30% observed with the sloped floor was mainly explained by the higher level of NH 3 -N emissions.