Changes in Serum Fatty Acid Composition and Metabolome-Microbiome Responses of Heigai Pigs Induced by Dietary N-6/n-3 Polyunsaturated Fatty Acid Ratio

Abstract

Changing fatty acid composition is a potential nutritional strategy to shape microbial communities in pigs. However, the effect of different n-6/n-3 polyunsaturated fatty acid (PUFA) ratios on serum fatty acid composition, microbiota, and their metabolites in the intestine of pigs remains unclear. Our study investigated the changes in serum fatty acid composition and metabolome-microbiome responses induced by dietary n-6/n-3 PUFA ratio based on a Heigai-pig model. A total of 54 Heigai finishing pigs (body weight: 71.59 ± 2.16 kg) fed with 3 types of diets (n-6/n-3 PUFA ratios are 8:1, 5:1, and 3:1) were randomly divided into 3 treatments with 6 replications (3 pigs per replication) for 75 days. Results showed that dietary n-6/n-3 PUFA ratio significantly affected biochemical immune indexes including glucose (Glu), triglycerides (TG), total cholesterol (TChol), non-esterified fatty acid (NEFA), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and total thyroxine (TT4), and medium- and long-chain fatty acid composition, especially n-3 PUFA and n-6/n-3 PUFA ratio in the serum. However, no significant effects were found in the SCFAs composition and overall composition of the gut microbiota community. In the low dietary n-6/n-3 PUFA ratio group, the relative abundance of Cellulosilyticum, Bacteroides, and Alloprevotella decreased, Slackia and Sporobacter increased. Based on the metabolomic analysis, dietary n-6/n-3 PUFA ratio altered the metabolome profiles in the colon. Moreover, Pearson's correlation analysis indicated that differential microbial genera and metabolites induced by different n-6/n-3 PUFA ratio had tight correlations and were correlated with the n-6 PUFA and n-3 PUFA content in longissimus dorsi muscle (LDM) and subcutaneous adipose tissue (SAT). Taken together, these results showed that lower dietary n-6/n-3 PUFA ratio improved serum fatty acid composition and metabolome-microbiome responses of Heigai pigs and may provide a new insight into regulating the metabolism of pigs and further better understanding the crosstalk with host and microbes in pigs.

Keywords: Heigai pig; fatty acid composition; metabolome; microbiome; polyunsaturated fatty acids.

FIGURE 1

Dietary n-6/n-3 PUFA ratio affects biochemical indexes in serum of Heigai Pigs. The contents of glucose [Glu, (A)], triglyceride [TG, (B)], total cholesterol [TChol, (C)], non-esterified fatty acid [NEFA, (D)], high-density lipoprotein [HDL, (E)], low-density lipoprotein [LDL, (F)], cortisol (G), immunoglobulin G [IgG, (H)], and total thyroxine [TT4, (I)] in serum from Heigai pigs fed with different diets. 8:1, 5:1, 3:1: different n-6/n-3 PUFA ratio diets. Data are presented as mean ± SEM (n = 6). *P < 0.05, **P < 0.01, ***P < 0.001.

FIGURE 2

Differences in the colonic bacterial α-diversity index after different n-6/n-3 PUFA ratio treatment. 8:1, 5:1, 3:1: different n-6/n-3 PUFA ratio diets. Data are presented as mean ± SEM (n = 5).

FIGURE 3

The relative abundance of bacteria in colonic digesta of Heigai pigs at the phylum, family and genus level. (A) Differential bacteria in colonic digesta at the phylum level. (B) Differential bacteria in colonic digesta at the family level. (C–H) The relative abundances of bacteria in colonic digesta at the genus level. 8:1, 5:1, 3:1: different n-6/n-3 PUFA ratio diets. Data are presented as mean ± SEM (n = 5). *P < 0.05, ^**P < 0.01.

FIGURE 4

The effects of dietary n-6/n-3 PUFA ratio on colonic metabolites. (A) Principal coordinates analysis (PCA) plot of colonic metabolites (ESI +) of Heigai pigs in different groups. (B) PCA plot of colonic metabolites (ESI-) of Heigai pigs in different group. The ellipse represents the 95% confidence interval of each group. (C,D) Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of these significant differential metabolites identified among three different groups under ESI + and ESI- modes. (E,F) Heatmap of colonic metabolites under ESI + and ESI- modes in each group. Only metabolites with P < 0.05 are displayed.

FIGURE 5

Correlations among meat quality, fatty acid profiles, the biochemical indexes in serum, differential microbiota at the genus level and bacterial metabolites in colonic digesta of Heigai pigs. (A) Correlations between meat quality, fatty acid profiles, the biochemical indexes in serum with differential microbiota at the genus level of Heigai pigs. (B) Correlations between meat quality, fatty acid profiles, the biochemical indexes in serum with bacterial metabolites in colonic digesta of Heigai pigs. Each square represents a Pearson correlation coefficient between a genus and an index, while the gradation of color represents the size of each correlation coefficient. The red color represents a positive correlation, while the blue color represents a negative correlation. pH, pH 45 min–pH 24 h; L, L 24 h–L 45 min; a, a 24 h–a 45 min; b, b 24 h–b 45 min. *P < 0.05, **P < 0.01.