Effects of Dietary Lysozyme Supplementation on Nitrogen Balance, Microbiota Diversity and Growth Performance of Growing Pigs

Abstract Lysozyme is an enzyme with antimicrobial properties that might improve gut health. This study aimed to evaluate the effect of lysozyme supplementation on growth performance, nitrogen (N) balance, and microbiota diversity of pigs and to determine the optimal inclusion level of this enzyme. Barrows [n = 72; 40.6 kg ± 2.6 body weight (BW); Yorkshire x Landrace] were used for this experiment. Pigs were distributed in a completely randomized design with 12 replicates within six dietary treatments (0, 16, 32, 48, 64, and 80 mg of lysozyme/kg of diet). Pigs were housed in the same pen, and individual transponders allowed feeders to identify the pigs, record their feed intake, and provide feed according to the individual assigned treatment. Animal growth performance was evaluated through average daily feed intake (ADFI, kg/d), average daily gain (ADG, kg/d), and gain-to-feed ratio (G:F, kg/kg) over 21 days. The N balance was estimated by dual-energy X-ray on days 1 and 21. The digesta in the jejunum segment was collected to study microbiota alpha and beta diversity. The linear-plateau and quadratic-plateau models were used to determine the optimal dietary lysozyme inclusion level as a function of ADG. The data were analyzed as completely randomized, the main fixed effect was lysozyme dose, and the scanning day was considered a random effect. The ADFI decreased linearly (P ≤ 0.01), while ADG, G: F and N utilization efficiency increased linearly (P ≤ 0.01) with the inclusion of lysozyme. Based on the non-linear models estimates, the minimal dietary lysozyme concentration maximizing ADG was 40 mg/kg, and no ADG response was observed above 50 mg/kg of supplementation. Shannon and inverse Simpson indices showed significant differences between cecum and jejunum (P ≤ 0.05) and due to the lysozyme, whereas treatments did not impact Chao1, ACE indexes and observed features, suggesting a treatment effect on species evenness but not on species richness. The treatments did not affect any of the beta diversity matrices analyzed. Based on these results, lysozyme supplementation up to 50 mg/kg may affect the species evenness in jejunum digesta while improving N utilization efficiency and ADG.