Effects of Different Net Energy Levels in Low-Protein Diversified Diets on Growth Performance, Nutrient...

In China, the application of low-protein, low-soybean meal diversified feeding strategies exhibits significant importance for reducing the dependence on soybean meal imports, lowering livestock and poultry feed costs, and decreasing nitrogen emissions from animal husbandry. Dietary protein content reduction modulates energy metabolism, while nonconventional feed ingredients alter energy efficiency. This study aimed to evaluate the effects of varying net energy (NE) levels on growth performance, nutrient digestibility, carcass characteristics, meat quality, and colonic microbiota in finishing pigs fed low-protein diversified diets. A total of 108 Duroc × Landrace × Yorkshire pigs (initial body weight: 79.8 ± 6.5 kg) were randomly assigned to six treatment groups: one control group fed a conventional corn-soybean meal diet with normal crude protein (CP) content and five groups fed low-protein diversified diets with different NE levels. The experiment was conducted over 49 days. During the 80-100 kg phase, pigs receiving the low-protein diversified diet exhibited a 9.12% improvement in feed-to-gain ratio (F/G) compared to the control group (p < 0.05). Additionally, dietary dry matter (DM) and ether extract (EE) digestibility significantly increased (p < 0.05). As NE levels increased under low-protein conditions, F/G decreased linearly (p < 0.05), while DM, gross energy (GE), EE, and CP digestibility showed significant linear and quadratic increase (p < 0.05). In the 100-130 kg phase (22-49 d), pigs in the low-protein diversified diet group demonstrated a 5.10% increase in average daily feed intake (ADFI) and an 8.60% increase in average daily gain (ADG), compared to the control group with normal CP content and the same NE level. Furthermore, dietary GE, EE, and CP digestibility improved significantly (p < 0.05). Under low-protein diversified diet conditions, as NE levels increased, F/G decreased significantly, ADFI decreased, and ADG increased to varying degrees. Similarly, DM, GE, EE, and CP digestibility showed significant increases. Carcass weight tended to increase linearly, while the slaughter rate initially increased before decreasing. Notably, low-protein diversified diets were associated with greater microbial community diversity in colonic digesta. The findings indicated that the optimal dietary NE for a low-protein diversified diet during the 80-100 kg phase was 9.84-10.21 MJ/kg, and 9.49-10.02 MJ/kg during the 100-130 kg phase. These results highlighted the importance of optimizing dietary NE levels in low-protein feeding strategies to enhance growth performance, nutrient utilization, and gut microbiota composition in finishing pigs.