The effect of fermented sea buckthorn products on production performance, egg quality, intestinal health, and antioxidant capacity of laying hens.

This study explored fermentation's effects on sea buckthorn metabolites and impacts of fermented products (hereafter referred to as microbial source antioxidant-MA) on laying peak period hens under varying nutrition, focusing on production performance, egg quality, gut health, and antioxidant capacity. A 2 × 3 factorial trial with 960 34-week-old Hy-Line hens employed two nutritional levels (CON: 16.50 % CP, 11.30 MJ/kg ME; LN: 16.00 % CP, 10.95 MJ/kg ME) and three MA doses (0, 350, 750 mg/kg) over 12 weeks. Metabolomics showed fermentation enriched sea buckthorn with antioxidants and anti-inflammatories (e.g., caffeate, quinic acid) and generated 1,134 differential metabolites, mainly in alanine, aspartate and glutamate pathways. LN reduced laying rate, egg mass (at all stages), egg weight (9-12 weeks and 1-12 weeks) and feed efficiency (PLevel<0.05); impaired egg quality (lower albumen height, Haugh unit, albumen ratio) at 4th week (PLevel<0.05); increased eggshell ratio and yolk ratio at 12th week (PLevel<0.05). LN increased in cecal propionic acid, butyric acid, and total volatile fatty acids (PLevel<0.05); upregulated jejunal TNF-α mRNA expression, downregulated Occludin (PLevel<0.05); and reduced enrichment of Halobacterota and Fusobacterium (PLevel<0.05) in cecum. Focusing on MA supplementation significantly increased the laying rate (1-12 weeks) and egg mass, and reduced the FCR (5-12 weeks) and the rate of unqualified eggs (5-8 weeks) (PMA<0.05); increased albumen height and Haugh unit at 4th week (PMA<0.05). It increased serum GSH and CAT, lowered serum MDA (PMA<0.05); increased ovarian GSH, CAT, GSH-PX, GSH-ST, and reduced ovarian MDA (PMA<0.05). MA reduced cecal pH (PMA<0.05); downregulated jejunal IL-6 and TNF-α expression, upregulated ZO-1 (PMA<0.05); and increased cecal Firmicutes, Fusobacterium, and Lactobacillus (PMA<0.05), with the 750 mg/kg dose being more effective (PMA<0.05). The addition of MA was negatively correlated with liver MDA (P < 0.01, R<-0.6), positively correlated with liver GSH and blood GSH (P < 0.01, R > 0.6), and positively correlated with ovarian CAT (P < 0.01, R > 0.6). MA exerted more significant effects on ovarian MDA and T-SOD, and more prominently increased the abundance of desulfobacterota under the LN level; whereas under the CON level, MA showed a stronger promoting effect on Fusobacterium abundance (PLevel*MA<0.05). In summary, fermentation enriches sea buckthorn with antioxidant and anti-inflammatory metabolites. The LN diet resulted in lower laying performance and egg quality during peak stage of laying hens. Dietary MA supplementation improves laying hens' production performance and egg quality by reducing the secretion of intestinal pro-inflammatory factors, maintaining intestinal barrier function, modulating the abundance of beneficial bacteria, and enhancing systemic antioxidant capacity (particularly in the liver and ovary). These benefits are dose-dependent and more pronounced in LN group hens compared to the CON group.