Age-related changes in the metabolism and stress biomarkers of breeder hens.

Our study aimed to evaluate reference intervals, interrelationships and changes over the lifespan of different metabolic and stress biomarkers of two different genetic lines of breeder (grandparent) hens (one female line, n = 290 and one male line, n = 290), either in blood or feather. Serum metabolic biomarkers included total proteins, albumin, uric acid, total cholesterol, high- and low-density lipoproteins (HDL-c and LDL-c), triglycerides, glucose, and non-esterified fatty acids. Stress biomarkers included feather corticosterone and the heterophil-to-lymphocyte (H:L) ratio in blood. Age markedly influenced all biomarkers, specifically with significant and progressive increases in lipids and proteins related to aging and more marked fluctuations in glucose and non-esterified fatty acids (NEFA). Feather corticosterone also increased progressively over time, whilst no significant age-related differences were detected for the H:L ratio. Significant differences were observed between pre-laying and post-laying periods for most biomarkers, except for NEFA and H:L ratio, reflecting the increased metabolic demands associated with the onset and maintenance of egg production. Correlation analyses revealed significant associations between metabolic and stress biomarkers, suggesting an interaction between metabolic status and stress response. Overall, these findings improve the understanding of age-related changes in metabolism and stress physiology in breeder hens and provide reference values that may support health monitoring, nutritional adequacy, welfare assessment, and the development of more sustainable poultry production systems.