Age-related changes in the transcriptomic profile associated with ovarian small white follicle recruitment in commercial laying hens

Egg production efficiency in poultry relies on the number of ovarian follicles selected for ovulation or atresia. Hens experience a gradual decline in reproductive efficiency as they age. However, the molecular mechanisms responsible for the decrease in small white follicles with age remain poorly understood. This study aimed to identify genes and biological pathways regulating the recruitment of small white follicles across different production cycles. Hy-line W-36 laying hens were obtained from a commercial poultry farm in three different age groups (n=15/group): 37 weeks (peak laying phase) as a control, 67 weeks (intermediate laying phase), and 87 weeks (late laying phase). Small white follicles from the ovaries (n =15/group) were collected for transcriptomic analysis. Total RNA was isolated from small white follicles (n =5/group) and analyzed using RNA sequencing and qPCR. RNA-seq data were analyzed to identify differentially expressed genes (DEGs), with a log2 fold change ≥ 2 for upregulated genes and ≤ -2 for downregulated genes (p-value < 0.05). This analysis revealed 118 DEGs in the 67-week group and 180 DEGs in the 87-week group. Key downregulated genes in the 67-week group include ATP6V1C1 and ATP6V0E1 (involved in receptor-mediated endocytosis), COX7C (regulates mitochondrial function and oxidative stress), and CIT (involved in cell division and proliferation). Key downregulated genes in the 87-week group are BCL9 (a co-activator in the Wnt/β-catenin signaling pathway), CLEC16A (involved in autophagy and mitophagy), and mTOR (involved in energy homeostasis, cell growth, proliferation, and mitochondrial function). Inhibitory pathways related to ovarian follicular recruitment include estrogen receptor signaling, adrenergic receptor signaling pathway, and serotonin receptor signaling in the 87-week group. Mitochondrial dysfunction was observed in both groups, and the CLEAR signaling pathway was activated in the 67-week group. This study reveals that mitochondrial dysfunction, hormone signaling pathways, and apoptosis contribute to reduced ovarian follicular recruitment in aging hens.