The Effects of Lactobacillus-Fermented Feed Derived from Tibetan Black Pigs and Changbai Mountain Wild Boars on the Growth Performance, Meat Quality, and Immune Function of Duroc × Landrace × Yorkshire (DLY) Finishing Pigs

To develop green feed additives suitable for antibiotic-free livestock farming on the Qinghai–Tibet Plateau, this study used Lactobacillus salivarius TB2.1, isolated from Tibetan black pigs, and Lactobacillus agilis CW13.2, isolated from wild boars in the Changbai Mountains, to prepare fermented feed. The study investigated the effects of these additives on the growth performance, slaughter performance, meat quality, immune and antioxidant functions, and gut microbiota composition of Duroc × Landrace × Large White crossbred finishing pigs (DLY finishing pigs). The experiment included 72 finishing pigs with an average body weight of 54.07 ± 1.02 kg, which were randomly divided into three groups, each with four replicates of 6 pigs. The control group (CK) was fed a basal diet, one treatment group (TB) was fed a diet consisting of 50% basal diet plus 50% Lactobacillus salivarius TB2.1-fermented feed, and the other treatment group (CW) was fed a diet consisting of 50% basal diet plus 50% Lactobacillus agilis CW13.2-fermented feed. The pre-feeding period lasted 3 days, and the experimental period lasted 57 days. The results showed that, compared with the CK group, (1) the CW and TB groups had significantly higher levels of crude protein, lactic acid, acetic acid, and propionic acid in the feed (p < 0.05), and significantly lower levels of crude fiber, neutral detergent fiber, acid detergent fiber, ammonium nitrogen, and pH (p < 0.05); (2) in the CW and TB groups, final body weight, average daily weight gain, and average daily feed intake were significantly higher (p < 0.001), while the feed-to-gain ratio was significantly lower (p < 0.01), with the CW group performing better than the TB group; (3) in both the CW and TB groups, carcass weight, eye muscle area, and meat redness significantly increased (p < 0.001), while backfat thickness and shear force significantly decreased (p < 0.001); (4) in both the CW and TB groups, serum immunoglobulin G, interleukin-2, and superoxide dismutase levels significantly increased (p < 0.05), malondialdehyde levels were significantly reduced in the CW group (p < 0.05), and catalase activity was significantly increased in the TB group (p < 0.05); (5) the relative abundance of Escherichia spp. in the cecum was significantly reduced in both the CW and TB groups (p < 0.05), while beneficial bacteria such as Lactobacillus spp. were significantly enriched (p < 0.05). In summary, feed fermented with Lactobacillus salivarius TB2.1 and Lactobacillus agilis CW13.2 can effectively improve the production performance of finishing pigs, enhance meat quality, strengthen immune and antioxidant capacities, and optimize the gut microbiota structure. Among these, CW13.2 was more effective in promoting weight gain, while TB2.1 was more effective in regulating protein and lipid metabolism. Fermented feed produced with both strains shows promising application prospects and can provide high-quality microbial strains and technical support for antibiotic-free swine farming on the Qinghai–Tibet Plateau.