Optimizing gut microbial balance and growth performance in growing pigs through protease-supplemented low protein diets

Introduction Environmentally friendly pork production is crucial to the pig industry, where the enhancement of growth performance and feed efficiency with reduced environmental impacts is favored. This study aimed to evaluate the effect that protease supplementation in a low crude protein diet has on the growth performance, nutrient digestibility, nitrogen retention, and gut microbiome in growing pigs. Methods Eighty pigs (Landrace × Yorkshire × Duroc; 24.72 kg) were selected, and based on initial body weight and sex, randomly allocated to one of the following dietary treatments: H, 16% crude protein (CP) diet; L, 14% CP diet; L+E1, low CP diet + 0.1% protease; and L+E2, low CP diet + 0.2% protease. Each treatment comprised four replicates with five pigs per pen. Results Pigs fed a low CP diet with protease supplementation showed a significantly higher body weight, average daily gain, and feed conversion ratio than those fed a high CP diet. In addition, ammonia emissions were lower in the L+E2 group than in the L group. Based on microbiome analysis, the L+E1 and L+E2 groups showed an increased Firmicutes-to-Bacteroidota ratio and elevated expression of pathways related to carbohydrate metabolism, coinciding with higher concentrations of short-chain fatty acids, such as butyrate and propionate, which support intestinal health. Additionally, the predicted function of the microbiota of pigs fed protease exhibited reduced nitrogen and sulfur metabolism, suggesting a potential reduction in excreted odorous compounds. Discussion These findings highlight the role of protease in enhancing growth performance and feed efficiency by modulating gut microbial composition and metabolic functions and reducing noxious gas emissions. Also, potential feed-cost savings are inferred from lower CP formulation.