Gaseous emissions from group-housed gestating sows kept on deep litter and offered an ad libitum high-fibre diet

Gaseous emissions from agriculture contribute to a number of environmental effects. Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) are greenhouse gases taking part in the global problem of climate change. Ammonia (NH₃) emissions are responsible of soil and water acidification and eutrophication and contribute also to indirect emissions of N₂O. The objective of this study was to investigate the effects of a high-fibre diet offered ad libitum to gestating sows on gaseous emissions (NH₃, N₂O, CH₄, CO₂ and water vapour (H₂O)). Four successive batches of 10 gestating sows were used for this trial. Each batch was divided into 2 homogeneous groups randomly allocated to a treatment: restricted conventional cereals based diet or high-fibre diet based on sugar beet pulp (42%). The groups were separately kept in two identical rooms equipped with a straw-bedded pen of 12.6m². For restricted sows, meals were provided once a day in individual feeding stalls available only during the feeding time. In both rooms, ventilation was automatically adapted to maintain a constant ambient temperature. The gas emissions were measured by infrared photoacoustic detection during 6 consecutive days at the 6th, 9th and 12th weeks of gestation. Sows performance (body weight gain, backfat thickness, number and weight of piglets) was not significantly different according to the diet. With sows offered high-fibre diet and compared to sows offered restricted diet, gaseous emissions were significantly greater for NH₃ (9.64g NH₃-N d⁻¹ sow⁻¹ vs. 5.37g NH₃-N d⁻¹ sow⁻¹; P <0.001), CH₄ (17.20gd⁻¹ sow⁻¹ vs. 15.21gd⁻¹ sow⁻¹; P <0.01), CO₂ (3.00kgd⁻¹ sow⁻¹ vs. 2.41kgd⁻¹ sow⁻¹; P <0.001) and H₂O (4.71kgd⁻¹ sow⁻¹ vs. 3.68kgd⁻¹ sow⁻¹; P <0.001) and significantly lower for N₂O (0.97g N₂O-Nd⁻¹ sow⁻¹ vs. 2.48g N₂O-Nd⁻¹ sow⁻¹; P <0.001) and CO₂ equivalents (0.88kgd⁻¹ sow⁻¹ vs. 1.55kgd⁻¹ sow⁻¹; P <0.001). In conclusion, the effects of high-fibre diet offered to gestating sows on deep litter on environment seem ambiguous with an increase of NH₃ emissions but a decrease of N₂O and CO₂ equivalent emissions.