Soya saponin improves egg-laying performance and immune function of laying hens

Abstract

Background: Soya saponin (SS), an active compound in soybean meals, has been widely studied in the medical field. However, it was considered as an anti-nutritional factor in poultry diets. The objective of this experiment was to measure the effects of dietary SS using three dietary treatments on egg-laying performance and immune function of laying hens. Birds were fed a low soybean meal basal diet (CON), a low-SS diet (50 SS) containing 50 mg/kg SS, or a high-SS diet (500 SS) containing 500 mg/kg SS for 10 weeks. At the end of the 5th and 10th week of the trial, samples were collected for analysis.

Results: Results showed that with 50 mg/kg SS supplementation, the egg production rate, feed conversion ratio (FCR), and eggshell quality tended to be improved. Serum follicle stimulating hormone (FSH) and Interleukin-4 (IL-4) levels were also elevated as well as the peripheral blood LPS stimulation index, the proportion of B lymphocytes, and antibody titer of bovine serum albumin (BSA). We also found that mRNA levels of follicle stimulating hormone receptor (FSHR) in ovarian, nuclear transcription factor kappa B (NF-κB), Transforming growth factor (TGF-β) and interferon γ (IFN-γ) in spleen were up-regulated at the end of the trial. Additionally, dietary 50 mg/kg SS improved the ileal flora via up-regulating the relative abundance of Lactobacillus, Romboutsia and Lactobacillus delbrueckii. Although the immune related indicators were improved with 500 mg/kg SS supplemented, it seemed to have a negative influence on the laying-performance. Specifically, serum alanine aminotransferase (ALT), alkaline phosphatase (ALP), and the ratio of IFN-γ to IL-4 were increased in the 500 SS group at the end of the trial. The mRNA levels of gonadotropin releasing hormone 1 (GnRH1) in Hypothalamus, the estrogen related receptor (ERR) in ovaries were downregulated as well as the egg production rate during the trial with 500 mg/kg SS supplemented.

Conclusions: The egg production performance was improved by dietary supplemented with 50 mg/kg SS via increasing ovarian FSHR transcription level and serum estrogen level. A beneficial shift in intestinal microflora was recorded, and the immune function of laying hens was also improved with 50 mg/kg SS supplementation. Surprisingly, the long-term supplementation of 500 mg/kg SS exerted a negative impact on the laying performance and physiological functions of the liver of laying hens.

Keywords: Egg-laying performance; Immune function; Laying hens; Soya saponin.

Fig. 1

The effects of SS on laying rate and body weight of laying hens. The above A, B, C, and D represented the results of body weight, egg production rate, average egg production rate, the ratio of feed to egg (FCR), and average egg weight during the experiment. Among them, * was judged as a significant difference (0.01 < P < 0.05), the same below, (n = 6)

Fig. 2

The effect of SS on the gene mRNA levels about hypothalamus and ovary. The above A and B represented the results of gene mRNA levels about hypothalamus and ovary at the end of the trial. Among them, ** represents an extremely significant difference (P < 0.01), the same below (n = 8)

Fig. 3

The effects of SS on peripheral blood lymphocyte ratio, stimulation index, and the antibody titer of BSA. Peripheral blood lymphocyte stimulation index and lymphocyte ratio at the end of 5th week were showed in A and B, (n = 6). C and D showed the peripheral blood lymphocyte stimulation index and lymphocyte ratio at the end of 10^th week, (n = 8). The results of BSA antibody titer were showed in E, (n = 8). Among them, ** represents an extremely significant difference (P < 0.01), * was judged as a significant difference (0.01 < P < 0.05), the same below. Our analysis steps for flow cytometry results were as follows. At first, we use the CD45 ring gate to eliminate the interference of red blood cells. In the gate of CD45⁺, T lymphocytes were labeled with CD3⁺ and their ratios were obtained. B lymphocytes and monocytes were labeled with Bu1⁺ and Mon⁺, and their ratios were obtained. The detailed flow analysis density map could be tracked in supplementary Figs. 1 and 2

Fig. 4

The effect of SS on the microbial structure of the ileum of laying hens at the end of the 5th week (27 week old). A, B, C, D, and E represented the α-diversity of the flora, the venn diagram of different species, the β-diversity (PcoA), the cluster structure of the flora, and the results of the differential flora analyzed by LEFSe. Among them, WCTR = Control, WC50SS = 50 ppm SS, WC500SS = 500 ppm SS (n = 6)

Fig. 5

The effect of SS on the relative abundance of bacteria at different classification levels at the end of 5th week (27th week). The above figure 5A, 5B, and 5C respectively represent the relative abundance results of ileal flora at the phylum, genus and species level. Among them, CTR = Control, W50SS = 50 ppm SS, W500SS = 500 ppm SS (n = 6)

Fig. 6

The correlation analysis results between intestinal bacteria and immune-related indicators at the end of 5th week (27 week old). The results of the correlation analysis between the immune-related indicators and the bacteria with differences at the end of 5th week were showed in Fig. 6. Among them, * represents a significant difference (0.01 < P < 0.05), and ** represents an extremely significant difference (P < 0.01)

Fig. 7

The effect of SS on the gene mRNA levels and morphology of liver. The above A and B represented the results of gene mRNA levels about liver at the end of the trial. The morphological observation results about the liver at the end of the trial were showed in C above. The arrow points to the infiltration of immune cells. Among them, ** represents an extremely significant difference (P < 0.01), * was judged as a significant difference (0.01 < P < 0.05), the same below (n = 8)

Fig. 8

The effect of SS on the gene mRNA levels of spleen. The results of gene mRNA levels about spleen at the end of the trial were showed in the above A and B. Among them, ** represents an extremely significant difference (P < 0.01), * was judged as a significant difference (0.01 < P < 0.05), the same below (n = 8)

Fig. 9

Correlation analysis between serum biochemical indicators and egg production performance at the end of the trial. The results of correlation analysis between serum biochemical indicators and egg production performance at the end of the trial were showed in Fig. 9. Among them, * represents a significant difference (0.01 < P < 0.05)