Impact of pig diets with different fibre contents on the composition of excreta and their gaseous emissions and anaerobic digestion

Two diets with the same net energy and digestible lysine content were compared in growing pigs: a control diet with soybean meal as the main protein source, and an experimental high fibre (HF) diet with 15% of dried distiller's grain with solubles and 15% rapeseed meal as the main protein source. The animals (10 castrated males) were housed individually in metabolism cages, and urine and faeces were collected separately from each pig in order to measure nutrient digestibility and the excretory patterns of nitrogen (N) and carbon (C). Ammonia (NH₃) volatilisation was measured from samples of slurry and urine, over a 16-day storage period in a laboratory pilot scale system. The methane (CH₄) production from effluents (fresh faeces and slurry) was measured using three methods: a biomethanogene test to obtain the ultimate CH₄ potential (B₀), a simulation of storage over 100 days, and with a lab scale anaerobic digester. The addition of biofuel by-products as fibre source had no significant effect on the animal growth performance, but it significantly reduced organic matter (OM), N and C digestibility by 7%, 8% and 9%, respectively. The HF diet significantly increased the amount of faeces excreted by 40%, whereas the amount of urine was not affected. Concurrently, the HF diet significantly increased the C content of the faeces by 51% and the amount of OM excreted per pig by 65%, compared to the control diet. NH₃ emissions from slurry and urine were significantly reduced for the HF diet by 31% and 26%, respectively, compared to the control diet. The B₀ expressed in L CH₄kg⁻¹ OM was not affected by the type of diet. During the simulation of storage, the CH₄ production expressed in L CH₄kg⁻¹ OM was significantly affected by the diet and the type of effluent. With the lab-scale anaerobic digester, CH₄ production per kg OM was higher for faeces than for slurry (333Lkg⁻¹ OM vs. 219Lkg⁻¹ OM, respectively) whereas the difference between the HF and the control diet was small.