The effect of broiler breeder maternal age on gene expression of the hen and the embryo

Background: Broiler breeder hens begin lay at approximately 25 wk of age and produce small eggs that are frequently non-settable or that 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 was to characterize differences in gene expression and protein abundance in breeder hens and their embryos.

Methods: Cobb 500 breeder hens were artificially inseminated at 26 and 35 wk of age, and hatching eggs were collected over a 7-d period at each age. Yolk sac and LV samples were taken from embryos at embryonic day 17 (E17), and abdominal fat (AF) and LV samples were taken 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 cut-off of 2.0 and P < 0.05. Selected targets were confirmed by Western blot.

Results: In the YS of embryos from 26-wk-old hens, the most over-expressed genes were PC, GPT2, and LPL, with fold increases of 75, 28, and 24. Three genes were under-expressed in the YS but over-expressed in the embryonic LV of the same embryos: FABP2, LRP2, and PKM2. In the LV of 26-wk-old hens, the most over-expressed genes were the fatty acid metabolism genes SCD, ELOVL6, and ACACA. Protein abundance confirmed greater GPT2, PC, and LPL in the YS of embryos from young hens, whereas LRP2 protein was greater in embryos from 35-wk-old hens.

Conclusion: Embryos from young breeder hens show greater expression of gluconeogenic and carbohydrate-related genes, whereas embryos from prime-aged hens show greater abundance of lipid transport proteins. These results indicate an age-related shift in fuel utilization during late incubation rather than impaired fatty acid metabolism.