Esperanza Fuertes ¹ Laura Sarri ^1* Rodrigo Carnicero ¹ Estefania Pérez-Calvo ² Álvaro Calderón ³ Joaquim Balcells ¹ Ahmad Reza Seradj ¹ Carlos Cantero-Martinez ¹ Jesús Fernández-Ortega ¹ Gabriel De La Fuente Oliver ^1*

• ¹ Universitat de Lleida, Lleida, Spain
• ² DSM (Switzerland), Basel, Switzerland
• ³ DSM (Spain), Madrid, Asturias, Spain

The environmental impact of livestock waste has driven the need for nutritional strategies to enhance digestive efficiency in pigs, aiming to reduce nutrient excretion and associated emissions of pollutants like ammonia (NH₃) and greenhouse gases (GHG). This study investigated the effects of dietary crude protein (CP) reduction by 1.5%, combined with supplementation of a dietary treatment that included feed additives and higher soluble fiber levels, on nutrient digestibility, slurry composition, and emissions across growing and finishing phases. Eighty male pigs were assigned to four different diets in a 13-week trial under a 2 × 2 factorial design: standard protein (SP) and low protein (LP) diets, with or without the dietary treatment. Key measurements included slurry composition, NH₃-N and CH₄ emissions, and crop yield when slurry was applied as fertilizer. The low-protein diet supplemented with additives (LPA) significantly reduced slurry pH (P ≤ 0.001) and urinary NH₃-N excretion (interaction, P = 0.03), improving nutrient digestibility and lowering organic matter content in slurry (P < 0.05). NH₃ emissions from the room and slurry pit decreased by over 38%, while CH₄ emissions, although higher in LP diets, were mitigated with the LPA diet. Field application of slurry as fertilizer resulted in trends favoring sustainable wheat production, with increased yield and nitrogen use efficiency, alongside reduced CH₄ emissions (P < 0.001). These findings underscore the potential of combined dietary strategies to mitigate environmental impacts while enhancing agricultural sustainability.