Mulberry branch fiber improved lipid metabolism and egg yolk fatty acid composition of laying hens via the enterohepatic axis

Abstract

Background: The utilization of mulberry branch fiber (MF), the largest by-product of the sericulture industry, is an important issue. Supplementation with MF as a dietary fiber for poultry may serve as a useful application. However, little is known about the effects of MF on liver lipid metabolism and egg yolk fatty acid composition of laying hens and their underlying mechanisms. In this study, we performed a multi-omics investigation to explore the variations in liver lipid metabolism, egg yolk fatty acid composition, gut microbiota, and the associations among them induced by dietary MF in laying hens.

Results: Dietary MF had no harmful effects on the laying performance or egg quality in laying hens. The enzyme activities associated with lipid metabolism in the liver were altered by the addition of 5% MF, resulting in reduced liver fat accumulation. Furthermore, dietary 5% MF induced the variation in the fatty acid profiles of egg yolk, and increased the polyunsaturated fatty acid (PUFA) content. We observed a significant reduction in the diversity of both gut bacteria and changes in their compositions after the addition of MF. Dietary MF significantly increased the abundance of genes involved in fatty acid biodegradation, and short-chain fatty acids biosynthesis in the gut microbiota of laying hens. The significant correlations were observed between the liver lipid metabolism enzyme activities of hepatic lipase, lipoprotein lipase, and total esterase with gut microbiota, including negative correlations with gut microbiota diversity, and multiple correlations with gut bacteria and viruses. Moreover, various correlations between the contents of PUFAs and monounsaturated fatty acids in egg yolk with the gut microbiota were obtained. Based on partial-least-squares path modeling integrated with the multi-omics datasets, we deduced the direct effects of liver enzyme activities and gut bacterial compositions on liver fat content and the roles of liver enzyme activities and gut bacterial diversity on egg yolk fatty acid composition.

Conclusions: The results indicate that dietary MF is beneficial to laying hens as it reduces the liver fat and improves egg yolk fatty acid composition through the enterohepatic axis. Video Abstract.

Keywords: Egg quality; Laying hen; Lipid metabolism; Multi-omics; Short-chain fatty acids.

Fig. 1

Scanning electron microscopy of MF. a 1000 × and b 5000 × magnifications

Fig. 2

Differences in the liver fat indices (a) and enzyme activities related to lipid metabolism (b) among laying hens with and without dietary MF. Different lowercase letters in each box of the same subfigure represent significant differences among laying hens in different groups (Tukey’s HSD test, p < 0.05). c Light micrographs of Oil red stain from liver of laying hens with MF addition compared to the CK samples

Fig. 3

a Differences in the fatty acid contents between the egg yolk of the CK and MF5 groups. b Principal coordinate analysis (PCoA) of the fatty acid profiles in egg yolk of the CK and MF5 groups based on the Bray–Curtis distance. Differences in the contents of SFAs (c), MUFAs (d), and PUFAs (e) between the egg yolk of the CK and MF5 groups. * represents significant differences between laying hens of the CK and MF5 groups (Student’s t test, p < 0.05)

Fig. 4

a Differences in the alpha diversity indices of gut bacterial and viral communities among laying hens with and without dietary MF. b PCoA and adonis test based on the Bray–Curtis distance of gut bacterial and viral communities among laying hens with and without dietary MF. c The difference in the Bray–Curtis distance of gut bacterial and viral communities among laying hens with and without dietary MF. d Variations in the relative abundance of Proteobacteria in the caecum digesta of laying hens with and without dietary MF. e Variations in the relative abundance of Ligamenvirales and Ortervirales in the caecum digesta of laying hens with and without dietary MF. Different lowercase letters in each box of the same subfigure represent significant differences among laying hens in different groups (Tukey’s HSD test, p < 0.05)

Fig. 5

a PCoA and adonis test based on the Bray–Curtis distance of gut microbial functions among laying hens with and without dietary MF. b The difference in the Bray–Curtis distance of gut microbial functions among laying hens with and without dietary MF. c The heatmap shows gut microbial functional pathways with different abundances among laying hens with and without dietary MF. Different lowercase letters in each box of the same subfigure represent significant differences among laying hens in different groups (Tukey’s HSD test, p < 0.05). d The network shows correlations among functional pathways with bacterial and viral genera in the caecum digesta of laying hens with and without dietary MF

Fig. 6

a PCoA and adonis test based on the Bray–Curtis distance of SCFA compositions in the caecum digesta between laying hens with and without dietary MF. b SCFAs with significantly different contents in the caecum digesta between laying hens with and without dietary MF. c PCoA and adonis test based on the Bray–Curtis distance of AA compositions in the caecum digesta between laying hens with and without dietary MF. d AAs with significantly different contents in the caecum digesta between laying hens with and without dietary MF. e The heatmap shows the abundance of genes related to the biosynthesis of SCFAs and the urea cycle in the caecum digesta of laying hens with and without dietary MF. Different lowercase letters in each box of the same subfigure represent significant differences between laying hens in different groups (Student’s t test, p < 0.05)

Fig. 7

a Heatmap showing correlations of gut microbiota, lipid metabolism indicators and fatty acid composition of egg yolk. Color in each block represents the correlation coefficient. *, **, and *** represent the p value lower than 0.05, 0.01, and 0.001, respectively. b Partial least-squares path modeling showing the effects of dietary MF on the health state and egg quality of laying hens. Only paths with significant tests (p < 0.05) are shown in the plot. Positive and negative effects are shown by red and black lines, respectively. The line width was assigned according to the correlation coefficient