Exploration of age-related changes in reproductive parameters of female Japanese quail (Coturnix japonica)

The decline in reproductive efficiency during post-peak period of production in poultry species holds significant economic implications. This study aimed to investigate the productive and reproductive performance of Japanese quails across distinct production stages and the association between these parameters and some genes expression and histometric alterations within the reproductive system. A total of 180 quails from a commercial flock were selected at varying egg production stages, including young, mature, and old, with 45 female and 15 male quails allocated to each group. The quails were maintained for six weeks. During recording period, daily records of egg production and egg weight were recorded. Additionally, oviduct histometric and Follicle biometric measurements, along with mRNA transcript abundance assessments related to follicular selection and yolk accumulation, were conducted on the oviduct, ovary, and small yellow follicles at the end of the experimental period. The results revealed a decrease in egg production in the old group compared to the young and mature groups (P < 0.05); meanwhile, the old group had the highest egg weight, and F1 follicle weight (P < 0.05). Additionally, the number of prehierarchical follicles was lower in the mature and old groups compared to the young group (P < 0.05). The lowest oviduct length, primary and secondary fold height, and thickness of the isthmus and magnum were noted in the old group (P < 0.05). Fertility and hatchability were lower in the old group compared to the other groups (P < 0.05). The mRNA transcript abundance of anti-Mullerian hormone (AMH), was highest in the old group and lowest in the young group (P < 0.05), while the mRNA transcript abundance of bone morphogenetic protein 15 (BMP15) was higher in the mature group compared to the other groups (P < 0.05). Additionally, the young quails had the highest occludin (OCLN) mRNA transcript abundance compared to other groups (P < 0.05). Overall, the study findings indicate decreased production and reproductive performance, as well as reduced hatchling quality over the production period, attributed to a declining number of follicles, noncooperative gene expression related to follicle selection and yolk accumulation, and diminishing oviduct fold size.