Characterization of persistency of lay in laying hens†

Selective breeding in laying hens has resulted in a laying rate of approximately one egg per day during their first year. Due to variability within a flock, egg-laying rates decline after the first year, leading producers to cull hens. The aim of this study was to identify physiological and molecular differences between persistent (PL, egg-laying rate = 100%) and non-persistent layers (NPL, egg-laying rate ≤82%) after the first year. Forty laying hens were reared from 16 to 76 weeks of age and a subset was maintained until 96 weeks. Throughout the study, egg-laying data were recorded daily, and plasma samples and body weights were collected once to twice monthly. At 76 weeks, PL (n = 7) and NPL (n = 6) hens were identified. PL hens were heavier than NPL hens starting at 36 weeks and triiodothyronine levels decreased in PL hens from 26 to 76 weeks. At 76 weeks, ovarian tissue was collected from PL (n = 3) and NPL (n = 4) hens for follicle counts, gene expression analysis, and histological analysis. PL hens had significantly more 3-5 and >12 mm follicles, higher anti-Mullerian hormone and bone morphogenic protein 15 mRNA expression, and lower atresia rates in follicles <100 μm, suggesting a larger remaining ovarian reserve than NPL hens. Ovarian RNA-sequencing analysis revealed 279 differentially expressed genes between PL and NPL hens and analysis predicted the estrogen receptor as an upstream regulator. A greater understanding of the physiology and molecular patterns of persistent hens could provide insights into ovarian aging and enhance production efficiency.