The change of albumen quality during the laying cycle and its potential physiological and molecular basis of laying hens

To elucidate the regulatory mechanisms that impact variability in albumen quality of laying hens from the peak of lay to the late production phase. A 60-wk study was conducted on a cohort of 20,000 Hy-Line Brown laying hens from 20 to 80 wk old. Before commencement at 20 wk, the 10-wk-old hens were acclimatized for 10 wk. This study examined changes in albumen quality, serum, and liver antioxidant capacity, magnum morphology, and expression of albumen-protein-related genes in the magnum. To reduce sampling error, we collected eggs (n = 90) from pre-determined cages at every sampling point (5-wk intervals), and 8 hens were selected at 10-wk intervals for blood and tissue collection. Our findings revealed that age significantly affected most evaluated parameters. Albumen gel properties, including hardness, gumminess, and chewiness, increased significantly with age (P < 0.05). With the increasing of hens' age from 20 to 80 wk, the albumen proportion of eggs was decreased, but eggshell proportion, yolk proportion, thick albumen proportion, thick to thin ratio, thick albumen solid content, albumen height, Haugh units (HU), and yolk color were increased and then decreased (P < 0.05). Compared to hens aged 20 to 60 wk, the hens (70-80 wk) had significantly reduced total antioxidant capacity (TAC) and glutathione levels (GSH) in the liver and lower serum TAC and superoxide dismutase levels (SOD) (P < 0.05). The magnum mucosal folds were highest in 40 to 60 wk-old hens, and the luminal diameter increased with age (P < 0.05). In the magnum, the mRNA expression levels for OVA, CPE, and NUP205 increased significantly between 30 and 40 wk, while FBN1 expression was higher between 30 and 50 wk (P < 0.05). At 70 to 80 wk, the expression of BRCA2 was significantly downregulated (P < 0.05). Albumen height, thick albumen proportion with protein secretion-related genes, enhanced antioxidant function, and luminal diameter correlated positively. However, the thick-to-thin albumen ratio negatively correlated with BRCA2, downregulated in aged laying hens. We used principal component and cluster analysis to deduce albumen quality changes during 3 phases: 25 to 35, 40 to 55, and 60 to 80 wk. The decline in albumen quality in aging hens is linked with decreased antioxidant capacity, magnum health, and downregulation of key genes involved in protein synthesis and secretion. These findings emphasize critical albumen quality changes in laying hens and suggest molecular pathways underlying age-related albumen quality alterations.