Dietary Net Energy Concentration Affects Growth Performance, Carcass Traits, Intramuscular Fatty Acid Profile, and Cecal Microbiota of Pigs with Restricted Feed Allowance

This study investigated the effects of different dietary net energy (NE) concentrations on the growth performance, carcass traits, meat quality, and cecal microbiota of feed restricted pigs. In total, 32 Sichuan-Tibetan black pigs with similar initial body weights (25.98 ± 0.27 kg) were divided into four groups: a control group (ad libitum feeding, 2330 kcal NE kg^-1) and three treatment groups (twice-daily feeding with NE concentrations of 2330, 2370, and 2410 kcal kg^-1, respectively). This feeding trial lasted for 19 weeks. Decreasing feeding frequency reduced the final body weight, average daily gain (ADG), average daily feed intake (ADFI), and backfat thickness (<i>p</i> < 0.05). Elevation of NE concentration increased the final body weight, ADG, and fat deposition (<i>p</i> < 0.05), which eventually led to an improvement in feed efficiency (<i>p</i> < 0.05). The expression of lipid-metabolism-related genes was significantly downregulated as NE concentration increased under a restricted feeding regime (<i>p</i> < 0.05). Cecal microbiota analysis showed that a high NE concentration decreased microbial alpha-diversity (<i>p</i> < 0.05). These findings suggest that under the restricted feeding condition, 2370 kcal NE kg^-1 can improve feed efficiency and optimize carcass composition simultaneously, which are associated with the changes in gut microbiota structure and the lipid-metabolism-related gene expression.