Effects of dietary fibres on gut microbial metabolites and liver lipid metabolism in growing pigs

Lactobacillus delbrueckii might lower serum triglyceride levels via colonic microbiota modulation and SCFA-mediated fat metabolism in parenteral tissues of growing-finishing pigs

Gut microbiota and its metabolites play a key role in host metabolism. Our previous study found supplemental Lactobacillus delbrueckii affected lipid metabolism of pigs, however, the underlying mechanism is unclear. In this study, we investigated the effects of L. delbrueckii on colonic bacteria composition and its metabolites, serum lipids and hormone levels, fat metabolism related enzyme activity and gene expression in various tissues of growing-finishing pigs. Twelve pigs were randomly distributed into two groups (n = 6), and pigs in each group were fed diets with (Con + LD) or without (Con) 0.1 % L. delbrueckii for 28 days. Results exhibited the deceased triglyceride (TG) levels and elevated free fatty acid (FFA) contents in serum and increased concentrations of butyric acid in colonic digesta after L. delbrueckii supplementation. Dietary L. delbrueckii increased abundance of Lactobacillus and Butyrivibri and tended to increase abundance of Akkermansia and Megasphaera in colonic digesta. L. delbrueckii consumption up-regulated glucagon-like peptide1 (GLP-1), monocarboxylate transporter1 (MTC1) and sodium-dependent monocarboxylate transporter1 (SMCT1) expression in colonic tissue. Administration of L. delbrueckii tended to increase lipoprotein lipase (LPL) activity, up-regulated CPT-1, angiopoietin-like protein 4 (Angpt14), LPL and triglyceride hydrolase (TGH) expression and down-regulated fatty acid synthetase (FAS), G protein-coupled receptor 41(GPR41) and GPR43 expression in the liver. L. delbrueckii addition increased adenosine monophosphate activated protein kinase (AMPK) expression in longissimus dorsi, upregulated LPL, CPT-1, Angptl4 and cluster of differentiation 36 (CD36) expression in subcutaneous fat, and enhanced LPL, CPT-1, TGH, adipocyte determination and differentiation-dependent factor 1 (ADD1) and hormone sensitive lipase (HSL) expression in leaf lard. These findings suggested that L. delbrueckii might enhance lipolysis and fatty acid β-oxidation to lower serum TG levels via colonic microbiota modulation and short chain fatty acids-mediated lipid metabolism of growing-finishing pigs.

Identifying key genes in milk fat metabolism by weighted gene co-expression network analysis

Milk fat is the most important and energy-rich substance in milk, and its content and composition are important reference elements in the evaluation of milk quality. However, the current identification of valuable candidate genes affecting milk fat is limited. IlluminaPE150 was used to sequence bovine mammary epithelial cells (BMECs) with high and low milk fat rates (MFP), the weighted gene co-expression network (WGCNA) was used to analyze mRNA expression profile data in this study. As a result, a total of 10,310 genes were used to construct WGCNA, and the genes were classified into 18 modules. Among them, violet (r = 0.74), yellow (r = 0.75) and darkolivegreen (r =  − 0.79) modules were significantly associated with MFP, and 39, 181, 75 hub genes were identified, respectively. Combining enrichment analysis and differential genes (DEs), we screened five key candidate DEs related to lipid metabolism, namely PI4K2A, SLC16A1, ATP8A2, VEGFD and ID1, respectively. Relative to the small intestine, liver, kidney, heart, ovary and uterus, the gene expression of PI4K2A is the highest in mammary gland, and is significantly enriched in GO terms and pathways related to milk fat metabolism, such as monocarboxylic acid transport, phospholipid transport, phosphatidylinositol signaling system, inositol phosphate metabolism and MAPK signaling pathway. This study uses WGCNA to form an overall view of MFP, providing a theoretical basis for identifying potential pathways and hub genes that may be involved in milk fat synthesis.

Carbohydrates effects on nutrition and health functions in pigs

The greatest improvement in carbohydrates studies on pig nutrition and health is that carbohydrates are classified more clearly, which is based not only on their chemical structure but also on their physiological characteristics. Besides its primary energy source, different types and structures of carbohydrates are a benefit for nutrition and health functions in pigs, which are involved in promoting growth performance and intestinal functions, regulating the community of gut microbiota, and modulating the lipids and glucose metabolism. The underlying mechanism of carbohydrates regulates the lipids and glucose metabolism through their metabolites (short-chain fatty acids [SCFAs]) and mainly via the SCFAs-GPR43/41-PYY/GLP1, SCFAs-AMP/ATP-AMPK, and SCFAs-AMPK-G6Pase/PEPCK pathways. Emerging research had evaluated an optimal combination in different types and structures of carbohydrates, which could enhance growth performance and nutrient digestibility, promote intestinal functions, and increase the abundances of butyrate-producing bacteria in pigs. Overall, compelling evidence supports the notion that carbohydrates play important roles in both nutrition and health functions in pigs. Moreover, identifying the carbohydrates combinations will be of both theoretical and practical values for developing the technology of carbohydrates balance in pigs.