Fermented Ginseng By-Products Regulate Calcium Metabolism Pathways, Liver Health, Immune Function and Intestinal Microbiota to Improve Eggshell Quality and Production Performance in Late-Laying Hens

High egg breakage during the late laying phase reduces the economic efficiency of egg production. This study investigated the effects of dietary supplementation with fermented ginseng by-products (FGB) on productive performance, eggshell quality, and related physiological indices in late-laying Roman Gray hens. A total of 360 hens (450 days old) were randomly assigned to four groups: a control group fed a basal diet and three treatment groups fed the basal diet supplemented with 100, 150, or 200 g/T FGB (GF100, GF150, and GF200, respectively). The trial lasted 90 days and was divided into early, middle, and late phases. FGB supplementation reduced the broken egg rate during the early phase, late phase, and overall trial period, increased average egg weight during the middle, late, and overall periods, and improved hen-day egg production during the late phase and across the entire trial. In addition, FGB increased eggshell weight during the early phase and increased eggshell thickness during the middle and late phases. FGB also upregulated several calcium metabolism-related genes in the duodenum and shell gland, particularly during the late phase, without causing consistent changes in serum calcium or inorganic phosphorus levels. Moreover, FGB altered serum biochemical indices in a phase-dependent manner and changed the relative abundance of several cecal genera. Overall, dietary FGB supplementation improved eggshell-related traits and productive performance in late-laying Roman Gray hens and was associated with changes in calcium metabolism-related gene expression, serum biochemical indices, and cecal microbiota composition.