Dietary Acidifier Modulates the Gut Microbiota–Metabolic Axis to Improve Intestinal Health, Yolk Fatty Acid Profiles, and Egg Quality in Laying Hens
Acidifiers are functional feed additives that may improve egg quality by modulating intestinal microbiota and host metabolism. This study investigated the effects of dietary acidifier supplementation on laying performance, yolk fatty acid composition, eggshell ultrastructure, intestinal function, cecal microbiota, serum metabolome, and antioxidant status in laying hens. Sixty 52-week-old Jingfen No. 6 laying hens were randomly assigned to either a control group or an acidifier-supplemented group for 6 weeks. Acidifier supplementation increased laying rate and egg mass while reducing the feed-to-egg ratio. It also increased the concentrations of seven yolk fatty acids, including tetradecanoic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, cis-vaccenic acid, and arachidic acid. In addition, acidifier supplementation resulted in a denser eggshell microstructure, improved cecal mucosal morphology, and enhanced the activities of lipase, chymotrypsin, amylase, and trypsin. Although cecal microbial alpha diversity remained unchanged, acidifier supplementation altered the overall microbial community structure and enriched several genera, including Slackia_A, Megasphaera_A, Veillonella_A, Merdimonas, and Caccocola. Serum metabolomic analysis identified 395 differential metabolites, primarily associated with lipid, amino acid, energy, and bile acid metabolism. Representative altered metabolites included taurodeoxycholic acid 3-glucuronide, LysoPE (0:0/20:0), 15-HETE, cholic acid, malic acid, and succinic acid. Acidifier supplementation also favorably affected serum HDL-C, LDL-C, and calcium concentrations and enhanced antioxidant capacity. Collectively, these findings indicate that dietary acidifier supplementation improves laying performance, yolk fatty acid deposition, eggshell structure, intestinal function, and antioxidant status, accompanied by alterations in cecal microbiota and serum metabolism. These coordinated changes may contribute to the observed improvements in egg quality.