Metformin alters liver metabolism to sustain egg production in the reproductively aging broiler breeder hen

The liver is critical in avian reproduction as it is the primary site of de novo lipogenesis and yolk precursor synthesis. Broiler breeder hens, the parents of commercial broiler chickens, have poor reproductive efficiency due to declining egg production from 45 weeks of age. We found that metformin increases fertile egg production in the aging broiler breeder hen, which was correlated with reduced body weight, reduced fat pad weight, and altered reproductive hormone profiles. This study aimed to characterize the liver transcriptome of the same broiler breeder hens supplemented with metformin in the diet at 0 or 75 mg/kg body weight for 40 weeks (25-65 weeks of age; n = 45 hens/treatment). Liver tissue was collected from a subset of hens (n = 12 hens/treatment group) at 65 weeks of age, and RNA was extracted and sequenced using next-generation sequencing. Differential gene abundance analysis revealed that metformin treatment led to significant changes in gene expression. Further transcriptomic analysis highlighted increased expression of genes related to estrogen-stimulated yolk precursor synthesis, insulin-stimulated de novo lipogenesis, and AMPK-mediated glucose homeostasis. Quantitative PCR analysis revealed increased expression of ESR1, APOB, APOV1, VTG2, ADIPOQ, ADIPOR2, and ACACA mRNA and decreased expression of PCK1 mRNA while plasma triglyceride and non-esterified fatty acid levels were lower in metformin-treated animals compared to controls. The present study suggests that metformin supplementation supports prolonged egg production in aging broiler breeder hens by sustaining yolk precursor and fatty acid synthesis that are typically diminished in aging broiler breeder hens.