Effects of Dietary Fiber and Copper on the Performance and Gut Microbiota of Finishing Pigs

This study aimed to investigate the effects of dietary fiber (DF) levels and copper concentrations on the production performance and cecal microbial diversity of finishing pigs. A 2 × 2 factorial experimental design was used, with different levels of dietary fiber (low [23% DF]: L and high [30% DF]: H) and copper concentrations (normal [25 mg/kg]: N and supplemented [45 mg/kg]: S) resulting in four diets (LN, LS, HN, and HS). Forty-eight hybrid barrows (Duroc × Landrace × Yorkshire), with an initial body weight of 76 kg ± 1.5 kg, were randomly assigned to four groups: LN, LS, HN, and HS, with 12 replicates per group and one pig per replicate. There was a 7-day adaptation period followed by a 56-day feeding trial, after which all pigs were slaughtered for sampling. Results indicated that in finishing pigs, the low dietary fiber group exhibited a higher final weight, a higher average daily gain, and a lower feed-to-gain ratio compared to the high fiber group (<i>p</i> < 0.05). The LS group showed higher digestibility of dry matter, crude protein, crude fiber, ash, neutral detergent fiber, and DF than the HN and HS groups (<i>p</i> < 0.05). Blood total protein levels were higher in the high fiber group, whereas blood Cu levels were higher in the supplemented copper group (<i>p</i> < 0.05). High dietary fiber increased the activities of colonic carboxymethylcellulase and β-glucanase (<i>p</i> < 0.05). Concentrations of acetic acid, propionic acid, and total volatile fatty acids were elevated in the high fiber group (<i>p</i> < 0.05). Microbial α-diversity indices (observed species, Chao 1, and Shannon indices) increased with fiber but decreased with copper supplementation (<i>p</i> < 0.05). The <i>Firmicutes</i>/<i>Bacteroidetes</i> ratio increased with fiber levels, with a higher relative abundance of Lactobacillus in the LS group. In conclusion, appropriate copper supplementation in diets can mitigate the negative effects of high fiber levels on finishing pig production performance by enhancing nutrient digestibility, fiber-degrading enzyme activity, regulating the microbial community, and its metabolic products.