Soy Saponin Improves Egg-Laying Performance and Immune Function of Laying Hens

Abstract Background It is of great significance to clarify the role of biologically active ingredients in soybean meal to solve the shortage of soybean meal resources. The objective of this experiment was to design a low soybean meal basal diet and measure the effects of dietary soya saponin (SS) on egg-laying performance and immune function. Results Results showed that egg production rate, feed conversion ratio (FCR), and eggshell quality tended to be improved in the 50 SS groups. Besides, peripheral blood LPS stimulation index and proportion of B lymphocytes ratio at 5th week were increased. Serum follicle stimulating hormone and Interleukin-4 (IL-4) levels were significantly elevated at 10th week in the 50 SS groups. We also found that mRNA levels of follicle stimulating hormone receptor (FSHR) in ovarian, nuclear transcription factor kappa B (NF-κB), Interleukin-12 (IL-12), Transforming growth factor (TGF-β) and Interferon γ (IFN-γ) in spleen were up-regulated at the end of the trial. Beyond that, the relative abundance of Proteobacteria in the ileal flora was dropped, and the relative abundances of Lactobacillus, Romboutsia and Lactobacillus delbrueckii were elevated in the 50 SS group. Similar to the above were that at the end of the 5th week, there are same biological effects on laying hens about 50 and 500 mg/Kg SS. While at the end of the trial, the blood levels of alanine aminotransferase, alkaline phosphatase, IFN-γ, and the ratio of IFN-γ to IL-4 were significantly increased in the 500 SS group. What’s more, the gene mRNA levels of NF-κB, IL-12, IFN-γ, Interleukin-1β (IL-1β), and the ratio of IFN-γ to IL-4 about spleen were up-regulated in the 500 SS group. The mRNA levels of genes such as the gonadotropin releasing hormone 1 (GnRH1) in Hypothalamus, the estrogen related receptor (ERR) in ovaries were down-regulated with 500 mg/kg SS supplementation. Conclustions: The egg production performance was improved by dietary supplementation with 50 mg/kg SS via stimulating ovaries development, increasing ovarian FSHR transcription level and serum estrogen level. The intestinal microflora was regulated, and the immune function of laying hens also was improved with 50 mg/kg SS supplementation. Unexpectedly, the immune homeostasis of the laying hens tilted towards the pro-inflammatory direction with 500 mg/kg SS supplementation. It resulted in a negative impact on the laying performance of laying hens and physiological functions of the liver.