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, this rate declines 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 T3 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 AMH and BMP15 mRNA expression, and lower atresia rates in follicles <100 μm, suggesting a larger 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 enhance production efficiency and provide insights into ovarian aging in women. Summary sentencePersistent laying hens have more prehierarchal and preovulatory follicles, lower incidence of atresia in <1mm follicles, and higher body weights than non-persistent laying hens which may contribute to higher egg-laying rates later in life.