A review of the structure and regulation of the laying hen's reproductive system and the interaction between the stress and reproductive axes.

Abstract

Abstract The laying hen's ovary is a unique biological model for studying the interaction of the reproductive (hypothalamic-pituitary-gonadal (HPG)) and stress (hypothalamic-pituitary-adrenal (HPA)) axes because of the highly regulated, grossly apparent hierarchical organization of ovarian follicles destined for maturation and ovulation. Additionally, the histological structure of the hen's pre-ovulatory hierarchical follicles allows for the manual separation of the theca and granulosa tissues with ease, making it an ideal model for conducting gene expression studies that are tissue-specific in avian species. Through follicular gene expression studies, the processes of vitellogenesis, follicular maturation, selection and ovulation have been thoroughly characterized in the laying hen. More recently, an interest in understanding the impact of stress on follicular development has arisen in the poultry industry given producers' desires to maximize production efficiency. Specifically, the role of glucocorticoids and the expression of glucocorticoid receptors (GRs) on avian ovarian follicles have been examined to closely assess the interaction of the HPG and the HPA axes. By understanding the interaction of these axes, a better understanding of the impact of stress on layer hens' ovarian function will be gleaned. In this review, the hen's reproductive system as well as reproductive and stress axes are covered extensively in order to provide insight into the dynamic interactions that exist between the hen's ovarian follicles and primary stress hormone, corticosterone.