The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Abstract

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Continuous exposure to red light induces photorefractoriness in broiler breeder pullets

“…Regardless, this is one of the first studies to report a disconnect between the timing of AFE and the E 2 peak. As E 2 is well established to be linked to the processes associated with initiating the production of all egg components ( Hanlon et al, 2022 ), this disconnect requires further investigation. Overall, this provides further evidence that the activation of the HPG axis has been impeded under continuous exposure to the supplemental red-light source.…”

RNAseq reveals modulation of genes involved in fatty acid biosynthesis in chicken liver according to genetic background, sex, and diet

“…BP_F, in both diet groups, showed a greater enrichment for oestrogen pathways because it was the most egg‐layer type chicken in the dataset. Indeed, oestrogen in laying hens stimulates the liver to synthesise FAs for egg enrichment (Hanlon et al, 2022). As reported by Ayers et al (2013), DE of genes related to the female W chromosome are essential for sex determination in chickens.…”

Impact of Glycetin Injection on Productive Traits in local Iraqi Chickens

“…In addition to estrogen's role in stimulating the VLDLR gene important in the growth and development of ovarian follicles [25], the Forkhead box12 gene, under the influence of the estrogen receptor, contributes to the basic regulation of egg production, growth and development of ovarian follicles, and ovulation events [ 26]. In order to avoid triglyceride breakdown during translocation to the follicle, the liver overexpresses VTG-II [27] and increases the production of ApoVLDL-II [28], an LPL inhibitor [29]. After sexual maturation, estrogen plays a key role in activating yolk precursors by increasing ApoVLDL-II and VTG-II gene expression [30,31].…”