Abstract
Hens in the late laying phase often experience age-related physiological constraints that may reduce production efficiency, eggshell quality, and welfare. This study evaluated the effects of dietary synbiotic supplementation on laying performance, egg quality, fecal characteristics, and the cecal microbiome of late-phase laying hens. A total of 240 Lohmann Brown hens (50 weeks old) were distributed into 20 replicates and randomly assigned to a corn-soybean control diet or the same diet supplemented with 100 mg/kg synbiotic (SYNLAC Prime®) for 22 weeks. Synbiotic supplementation did not affect egg production or egg mass but significantly reduced feed intake (P = 0.036). It also improved eggshell quality by decreasing the proportion of cracked eggs (P = 0.014) and increasing eggshell weight (P = 0.049) and shell thickness (P = 0.031). Fecal score and moisture content were not affected; however, synbiotic-fed hens showed lower fecal ammonia concentration (P = 0.033). Synbiotic supplementation increased both alpha and beta microbial diversity in the cecum. While microbial composition at higher taxonomic levels was largely unchanged, the relative abundances of Ruminococcaceae and Lachnospiraceae increased, whereas those of Bacteroidaceae and Clostridiaceae decreased. At the genus level, synbiotic supplementation increased Faecalibacterium, Ruminococcus, and Lactobacillus, while reducing Bacteroides and Alistipes. Functional prediction analysis indicated that synbiotic supplementation upregulated 12 cecal metabolic pathways and downregulated two pathways. Overall, synbiotic supplementation improved eggshell quality, promoted beneficial gut microbial populations, and reduced fecal ammonia emissions, suggesting its potential as a dietary strategy to support productivity and gut health in hens during the late laying phase.