Identification of the molecular networks governing ovulation frequency in low and high egg producing turkey hens

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dc.contributor.advisorPorter, Tom Een_US
dc.contributor.authorBrady, Kristen Marieen_US
dc.contributor.departmentAnimal Sciencesen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2019-10-01T05:34:25Z
dc.date.available2019-10-01T05:34:25Z
dc.date.issued2019en_US
dc.description.abstractSelection for carcass traits has negatively impacted and varied the reproductive efficiency of the commercial turkey hen, creating overall lowered egg production as well as distinct groups of low egg producing hens (LEPH) and high egg producing hens (HEPH). Ovulation frequency correlates with egg production and differs between LEPH and HEPH. Ovulation is governed primarily by the hypothalamo-pituitary-gonadal (HPG) axis through a preovulatory surge (PS) of luteinizing hormone (LH) and progesterone (P4) but ovulation can be influenced by the hypothalamo-pituitary-thyroid (HPT) axis. Dysregulation of the thyroid and reproductive axes, disrupting the PS, leads to lowered egg production, leaving the poultry industry to compensate with larger breeding flocks. LEPH exhibited hypothalamic and pituitary expression consistent with decreased ovulation stimulation and increased ovulation inhibition as well as decreased steroid synthesis in follicle cells. Neuroendocrine and ovarian tissues from HEPH showed a higher sensitivity and response to in vitro HPG axis stimulation. Moreover, cells from HEPH responded positively to HPG axis inhibition while cells from LEPH responded negatively, indicating functional differences in HPG axis regulation. RNA sequencing results reinforced the higher expression of HPG axis genes in HEPH and showed higher expression of HPT axis genes in LEPH. Estradiol (E2) was identified as an upstream regulator activated in HEPH. Hens with average egg production (AEPH) also showed upregulation of E2 receptors during the PS, suggesting involvement in positive feedback loops. Supporting the role of E2 in neuroendocrine feedback, higher plasma concentrations of E2 were seen during the PS in HEPH. Looking into the HPT axis, LEPH displayed lower plasma concentrations of triiodothyronine (T3) and higher levels of thyroxine (T4) outside of the PS while HEPH displayed lower levels of T3 and higher levels of T4 inside of the PS. The T3 and T4 levels surrounding the PS in HEPH were consistent with levels seen in AEPH. At a molecular, cellular, and endocrine level, the reproductive physiology of LEPH and HEPH differs, ultimately leading to egg production differences. Studies tying the noted differences to egg production rates will allow for identification of genetic markers to increase the reproductive efficiency of commercial breeding hens.en_US
dc.identifierhttps://doi.org/10.13016/jodj-n3jp
dc.identifier.urihttp://hdl.handle.net/1903/25099
dc.language.isoenen_US
dc.subject.pqcontrolledAnimal sciencesen_US
dc.subject.pqcontrolledMolecular biologyen_US
dc.subject.pqcontrolledEndocrinologyen_US
dc.subject.pquncontrolledEgg Productionen_US
dc.subject.pquncontrolledHPG Axisen_US
dc.subject.pquncontrolledHPT Axisen_US
dc.subject.pquncontrolledOvulationen_US
dc.subject.pquncontrolledSteroidogenesisen_US
dc.subject.pquncontrolledTurkeyen_US
dc.titleIdentification of the molecular networks governing ovulation frequency in low and high egg producing turkey hensen_US
dc.typeDissertationen_US

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