The Effect of Broiler Breeder Maternal Age on Gene Expression of the Hen and the Embryo

Background and Objective: Broiler breeder hens begin laying at approximately 25 weeks of age and produce small eggs that are frequently non-settable or yield small chicks with reduced livability. The yolk sac (YS) and liver (LV) are the primary tissues supporting nutrient utilization during embryonic development, and hen age affects yolk size and hatchling weight. The objective of this study was to characterize age-related differences in gene expression and protein abundance in breeder hens and their embryos. Materials and Methods: Cobb 500 breeder hens were artificially inseminated at 26 and 35 weeks of age, and hatching eggs were collected over a 7-d period at each age. Yolk sac and LV samples were collected from embryos on embryonic day 17 (E17), while abdominal fat (AF) and LV samples were collected from the hens that produced those eggs. Forty-eight genes related to fatty acid, glucose, and amino acid metabolism were profiled using a fold-regulation cutoff of 2.0 and p<0.05. Selected targets were subsequently confirmed by Western blotting. Results: In the YS of embryos from 26-week-old hens, the most overexpressed genes were Pyruvate Carboxylase (PC), glutamic-pyruvate transaminase 2 (GPT2) and lipoprotein lipase (LPL), with fold increases of 75, 28 and 24, respectively. Three genes were underexpressed in the YS but overexpressed in the embryonic LV of the same embryos: fatty acid-binding protein 2 (FABP2), low-density lipoprotein receptor-related protein 2 (LRP2) and PKM2. In the LV of 26-wk-old hens, the most overexpressed genes were the fatty acid metabolism-related genes stearoyl-CoA desaturase (SCD), fatty acid elongase 6 (ELOVL6), and acetyl-CoA carboxylase alpha (ACACA). Protein abundance confirmed greater levels of GPT2, PC and LPL in the YS of embryos from young hens, whereas LRP2 protein abundance was greater in embryos from 35-wk-old hens. Conclusion: Embryos from young breeder hens exhibit greater expression of genes involved in gluconeogenesis and carbohydrate metabolism, whereas embryos from prime-aged hens exhibit greater abundance of lipid transport proteins. These findings indicate an age-related shift in fuel utilization during late incubation rather than impaired fatty acid metabolism.