Ammonia, Nitrous Oxide, and Carbon Dioxide Emissions from Pig Production: An Exploratory Study on Single-Cell Protein Inclusion in Piglets’ Diet

In animal production, gases such as ammonia and greenhouse gases (GHGs) originate from wastes in three main compartments: the animal house of an experimental facility in Northern Italy, storage sites and the slurry-spreading process on cultivated soils. Dietary composition can influence slurry characteristics and gaseous emissions from pig production systems. This exploratory study investigated relationships among slurry composition, volatile fatty acids (VFAs), and gaseous emissions in weaned pigs fed either a conventional diet or a reformulated diet. Faecal samples produced by piglets fed two different diets were collected at three time points: 14, 28 and 42 d of age. Piglets were housed in 32 pens (2 animals per pen, with 16 pens per treatment) on a slatted floor and assigned to either a control diet (C) or a reformulated diet (T) including single-cell protein (SCP). The piglets were administered a starter phase (0–14 days) and a grower phase (14–42 days). Slurry samples were analysed for physicochemical parameters, VFAs, NH3, N2O, and CO2 emissions. The reformulated diet was associated with higher total Kjeldahl nitrogen and volatile solids, together with changes in VFA profiles characterised by lower acetic and propionic acids and relatively higher lactic and n-butyric acids. NH3 and CO2 emissions tended to be lower in the reformulated treatment, whereas N2O showed variable responses across sampling times. These findings indicate that dietary reformulation with SCP inclusion may influence manure characteristics and fermentation processes, with potential consequences for ammonia emission mitigation. Given the exploratory nature of the study and the non-iso-nutritional formulation of the diets, the results should be interpreted as treatment-level associations rather than evidence of direct causal effects. Further studies under controlled nutritional conditions are required to clarify the mechanisms linking dietary composition, manure properties, and environmental emissions in pig production.