Impact of Xylanase Supplementation on Nitrogen Utilization and Ammonia Emissions in Growing Pigs

Abstract Carbohydrases improve organic matter digestibility by breaking down non-starch polysaccharides, which increases the availability of energy and other nutrients such as nitrogen (N). Reducing N losses is an effective strategy to mitigate N impact (e.g., acidification and greenhouse gas (GHG) emission) on environmental footprint of swine production. This study aimed to evaluate the effects of xylanase supplementation on growth performance, N excretion, and gas emissions in growing pigs fed low-crude protein (CP) diets. Forty-eight pigs (initial BW = 39.91 ± 2.37 kg) were allocated to 4-pig emission chambers, assigned to three dietary treatments (n = 4 per treatment) for 30-day, following a completely randomized design: T1, positive control (adequate CP and net energy (NE); 16,3%, 2476 kcal/kg); T2, negative control (CP and NE reduced to 14.9% and 2426 kcal/kg without enzyme); and T3, negative control + xylanase (100 g/ton), an endo-1,4-β-xylanase (EC 3.2.1.8) of bacterial origin (Bacillus subtilis). Feed intake and body weight were recorded weekly to calculate N balance. Slurry volume was measured and slurry analysed. Gaseous emissions (ammonia, methane, CO2) were monitored continuously using an integrated gas analysis system. Slurry and emissions data were used to calculate total and ammoniacal N excretion. Statistical analysis followed a generalized linear model (GLM), considering treatment as a fixed effect. Differences among means were assessed by Tukey’s test, with significance declared at P 0.05. There was a tendency (P = 0.082) for a higher ADG in T4 (1.25 kg/d) vs T2 (1.15 g/d) while T1 was intermediate (1.19 g/kg) and average daily feed intake (2,21-2,31 g/pig) and feed conversion ratio (2.03–2.06) were not impacted. Xylanase supplementation significantly reduced total, fecal, urinary, and ammonia excretion compared with the positive control diet T1. Total N excretion per kg of gain decreased from 28.0 g in T1 to 22.9 g in T3 (P = 0.013), fecal N from 13.4 to 12.1 g (P = 0.013), urinary N from 14.6 to 10.8 g (P = 0.013), and ammonia–N emissions from 6.83 to 4.34 g (P = 0.014). The negative control (T2) presented intermediate values without statistical difference from T3. Although not significant the N efficiency increase from 47 to 49 to 50% in T1, T2 and T3 respectively in line with numerical improvement of ADG. No effect was observed on CH4 and CO2 emissions. As xylanase is known to increase the digestibility of energy, it is possible that in high performance pigs fed low CP diets, the supplementary energy has allowed better use of N. In sum, xylanase supplementation improves N balance in low-protein diet in comparison to the positive control resulting in lower N excretion and emissions while maintaining the performance of the animals.