UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Characterizing the hypothalamic-pituitary-gonadal axis in turkeys genetically selected for increased egg production(2020) Galleher, Catherine Elizabeth; Porter, Tom E; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within the United States, the turkey industry has historically focused on increased meat production. Studies have shown that there is a negative correlation between meat and egg production. Previous research in our laboratory compared high egg producing hens (HEPH) to low egg producing hens (LEPH). It was found that HEPH express increased levels of mRNA for genes associated with stimulating the hypothalamic-pituitary-gonadal (HPG) axis. We also demonstrated that the hypothalamic-pituitary-thyroid (HPT) axis exerts some effect on egg production. In order to increase our understanding of differences in egg production, we focused on a genetically selected line with increased egg production (E line) and a random bred control line (RBC1). Related to the HPG axis, differences were found related to steroidogenesis and feedback mechanisms. Within the HPT axis, the RBC1 line tended to have increased mRNA levels of genes associated with stimulation of the axis compared to E line.Item Identification of the molecular networks governing ovulation frequency in low and high egg producing turkey hens(2019) Brady, Kristen Marie; Porter, Tom E; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Selection 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.Item BIOLOGY AND MANAGEMENT OF REPRODUCTION IN CAPTIVE CRANES(2017) Brown, Megan Elizabeth; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There are 15 species of cranes found throughout the world, 11 of which are listed as vulnerable or endangered. All 15 species are currently managed in captivity; however, with increased threats to wild crane habitats and populations, ex situ management becomes increasingly critical as a hedge against extinction. Reproduction and the production of offspring is required to ensure self-sustaining populations managed in ex situ conservation breeding programs. However, current reproductive success of the endangered whooping crane (Grus americana), as well as other species, maintained ex situ is suboptimal and hinders population sustainability and reintroduction goals. The objectives of this dissertation were to 1) develop a cryopreservation protocol for crane semen to improve genetic management in endangered cranes, 2) investigated seasonal hormone patterns and measured the impact of captive environment on hormone production and reproductive behaviors, and 3) retrospectively examine the effect of bird as well as management variables on egg fertility in whooping cranes. The findings demonstrated that 1) sperm of both whooping and white-naped crane performed better following cryopreservation when dimethyl-sulfoxide is utilized as a cryoprotectant, 2) seasonal fluctuations occur in hormone production in both sexes, while addition of a water feature to captive enclosures stimulated reproduction in females, and 3) female specific variables had the greatest influence on probability of egg fertility. Overall findings will help whooping crane management Continued research into the mechanisms controlling sperm sensitivity to cryo-damage, egg production, and fertilization are necessary to mitigate reproductive problems in captive crane species.Item Neuroendocrine mechanisms underlying paternal experience-induced plasticity of the hippocampus(2016) Hyer, Molly Melissa; Glasper, Erica R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Evidence suggests that males, like females, undergo altered structure and function of the hippocampus postpartum, a brain region that regulates certain aspects of emotion, learning, and memory. These behaviors are beneficial for successful parenting. In maternal rodents, offspring contact contributes to postpartum hippocampal plasticity in both mothers and offspring. Fathers do not undergo pregnancy, parturition, or lactation, therefore, the impact of offspring on hippocampal plasticity is less clear. California mouse (Peromyscus californicus) fathers are highly paternal, making this monogamous species a good model of paternal care. In this species, between postnatal days 15 and 21 paternal behavior becomes more active (i.e. increased pup retrievals) to care for pups that are beginning to explore outside of the nest. I observed reduced anxiety-like behavior in fathers specifically within this temporal window. Concomitant with attenuated anxiety-like behavior, I found that fathers maintain survival of adult born neurons in the dentate gyrus of the hippocampus. Enhanced hippocampal plasticity is not restricted to adult neurogenesis, as dendritic spine density in the dentate gyrus is increased in fathers at this same time – an effect that lasts until weaning. When permanently separated from their offspring, fathers show increased passive stress coping and reduced spine density in the DG. Taken together, these data suggest that the degree of active father-offspring interaction significantly alters hippocampal plasticity in the father. Estradiol and its receptors have been implicated in alterations to anxiety and adult neurogenesis in both males and females. I observed that estrogen receptor β (Erβ) mRNA expression was elevated in whole hippocampal homogenates at PND 16 in fathers. Similarly, circulating estradiol was elevated at both PND 2 and PND 16. After inhibition of Erβ with the drug tamoxifen, the number of surviving adult born neurons was suppressed in fathers alone. Taken together, these data suggest that in fathers, hippocampal plasticity occurs concomitantly with active father-offspring contact and that this plasticity, at least structural, is driven by activation of Erβ. Understanding paternal experience-induced plasticity and the mechanisms that drive it, may help to prevent deficits in paternal behavior that can disrupt offspring development and contribute to emotional dysregulation in fathers.Item A NOVEL NON-LETHAL LAPAROSCOPIC APPROACH TO DETECT INTERSEX (TESTICULAR OOCYTES) IN LARGEMOUTH BASS (MICROPTERUS SALMOIDES) AND SMALLMOUTH BASS (MICROPTERUS DOLOMIEU)(2016) MacLeod, Alexander Hugh; YONKOS, LANCE T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The appearance of testicular oocytes (TO) in wild fish populations has received considerable attention in the scientific literature and public media. Current methods to quantify TO are lethal; instead, a non-lethal alternative was examined. Laparoscopic insertion into the genital pore allowed internal visualization of the gonad and detection of TO by collecting five testis biopsies in smallmouth bass Micropterus dolomieu and largemouth bass Micropterus salmoides. Overall, biopsies quantified similar levels of TO detection and severity to conventional transverse sectioning with less than 10% mortality. Suitability of surgical anesthetics, tricaine methanesulfonate and electronarcosis were examined in laboratory and field applications. Electronarcosis had the added benefit of rapid sex identification and immediate release of female fish with minimal trauma, representing significant benefits when sampling small or compromised populations. Laparoscopy may be useful for monitoring the prevalence and severity of TO in these fish species when lethal sampling is not a desired outcome.Item The role of the adrenal glands in the plasma and urinary electrolyte changes during moderate and severe anoxia(1951) Kline, Raymond Franklin; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item Contribution to the genetics of growth in chickens as influenced by the thyroid gland(1950) El-Ibiary, Hussein Mahmoud; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item An investigation of the morphological changes, hormonal influences, and genetic factors concerned in the response of young chickens to conditions of stress(1953) Garren, Henry Wilburn; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item Effects of thyroxine sex hormones, and stress on hormonal interactions as measured by gland and organ weights, metabolic rate, resistance to exhaustion, and adrenal histology of New Hampshire(1953) Conner, Mark Hale; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item The effect of posterior lobe extract, adrenalin, and pilocarpine on the response of the thyroid gland to the thyreoactivator hormone of the anterior lobe of the hypophysis(1936) Teitelbaum, Harry A.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
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