Improving Meat Quality and Lipid Metabolism of Finishing Pigs by Replacing Dietary Soybean Meal with Enzyme–Bacteria Co-Fermented Rapeseed Meal

This study aimed to investigate the effects of enzyme-bacteria co-fermented rapeseed meal (FRSM) on the growth performance, serum biochemical parameters, meat quality, and lipid metabolism of finishing pigs. A total of twenty-eight Duroc × Landrace × Yorkshire finishing pigs (4 months of age; initial body weight: 60.92 ± 1.08 kg) were randomly allotted to one of four dietary treatments for a 45-day feeding trial, consisting of corn-soybean meal diet (CSD) and three experimental diets in which 50, 75 and 100% of soybean meal in the corn-soybean diet was replaced with FRSM. Results showed that replacing soybean meal with FRSM had no negative effects on the growth performance of finishing pigs, maintaining average daily gain and feed efficiency (p > 0.05). Compared with the CSD group, the FRSM group exhibited lower serum cholesterol (p < 0.05). The serum low-density lipoprotein cholesterol, alanine aminotransferase, and urea content levels were lower in the FRSM75 or FRSM100 groups than in the CSD group (p < 0.05). Compared to the CSD, FRSM feeding increased the pH24h and triglyceride content but significantly decreased the drip loss, shear force and chewiness in longissimus thoracis et lumborum (LTL) muscle (p < 0.05). Importantly, compared with the CSD, FRSM feeding significantly lowered the muscle SFA/UFA ratio, increased the PUFA/SFA ratio, and elevated threonine and valine levels (p < 0.05). The FRSM100 group exhibited further increases in umami amino acids (AAs), total essential AAs, and total AAs (p < 0.05). Morphological analysis indicated that, compared to CSD, the FRSM100 group had a significantly reduced muscle fiber perimeter in the LTL muscle (p < 0.05). Moreover, FRSM feeding up-regulated the expression levels of MyHC I and MyHC IIa and the lipogenic genes FASN, SREBP1, and SCD (p < 0.05). These results indicated that compared with rapeseed meal, FRSM exhibited a positive effect on improving the meat quality and lipid metabolism in finishing pigs and can be used as a suitable alternative protein source for soybean meal in finishing pig diets.