Animal Sciences electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Division of Animal Sciences. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Morphology of the female reproductive organs of sea otters (Enhydra lutris L.)(University of Missouri--Columbia, 1965) Sinha, Akhouri Achyutanand; Conaway, Clinton H."The purpose of this study was to investigate the gross and microscopic anatomy of the reproductive organs of the female sea otter (Enhydra lutris L.) and relate them to the reproductive cycle. Emphasis has been given to ovarian histology. Although the value of the sea otter has been known to fur hunters for over two centuries, very little is known about this animal. Barabash-Nikiforov (1947) noted that sea otters have lentioulate shaped ovaries. Pearson (1952) studied a single pregnant sea otter and noted that the ovaries have irregular surface and subsurface fissures, besides the small Graafian follicles and a corpus luteun. The uterus was bipartite. Lensink (1962) briefly described reproduction in sea otters, based upon field observations."--Introduction.Item The influence of the bursa on Fabricius, spleen and thymus on the course of Plasmodium lophurae infections in chickens(University of Missouri--Columbia, 1968) Longenecker, Bryan M.; Breitenbach, Robert P."Splenectomized chicks were severely deficient in their ability to combat an infection or reinfection with Plasmodium lophurae. Infection of splenectomized chicks usually caused death while sham-operated controls recovered. Birds splenectomized on the 5th day of an infection, when parasitemias had dropped to a low level, showed an immediate and usually fatal recrudescence. Chicks which were hormonally or surgically bursectomized on the 1st day after hatching demonstrated higher parasitemias then their sham-operated controls. However, parasitemias of birds bursectomized at 18 days of age did not differ from their control group. Thymectomy had no significant effect on the resultant parasitemias. It is thus concluded that the spleen is of primary importance in the development of immunity to this strain of Plasmodium lophurae. The bursa is of secondary importance and contributes something to the development of the immune mechanism before 18 days of age. Bursaless birds demonstrated higher initial gamma-1, beta-1, beta-2, alpha-1 and alpha-2 values than sham operated control groups. These high mean values in the bursaless birds decreased during the malarial infection to a low level on about day four of the infection. The infected control group showed no decrease; in fact, an increase was often observed in this group. On the other hand, low albumin and gamma-2 titers were obtained in the bursaless groups. These altered protein changes were most apparent in the hormonally bursectomized groups, and especially in the thymectomized-hormonally bursectomized group. The plasma protein values of the thymectomized group were similiar to those of the sham operated infected birds. The major plasma protein response to the injected malarial parasites in the sham operated infected group was an increase in gamma-1 globulin. An early peak was noted on day two of the infection as well as an increase from day ten to fifteen. This response did not appear in any of the bursaless groups or in the non-infected group. The possible significance of a relationship between the high alpha and low gamma-2 globulin levels of bursaless birds is discussed. Antimalarial antibodies were detected in the plasma of normal birds which recovered from infection with P. lophurae. These antibodies were detected as specific antiparasitic agglutinins in normal birds. These agglutinins were not detected in the plasma of bursaless birds which had been infected and reinfected. The administration of hyperimmune plasma to bursaless and normal birds resulted in highly depressed parasitemias. Interestingly, infected bursaless birds which were given normal plasma from mature cockerels demonstrated parasitemias which were depressed to the level of parasitemias of intact infected birds. This indicated that bursaless birds lack a natural antibody which birds normally develop. Splenectomized-infected birds which received hyperimmune plasma eventually recovered from an infection. Splenectomized—controls, however, succumbed to the infection. The surviving splenectomized birds subsequently demonstrated an ability to control the parasites, as attempts to reinfect these birds failed. It was postulated that in the absence of the spleen and during intense antigenic stimulation, other lymphoid centers develop which are able to participate in normal anamnestic reactions."--Summary.Item Impact of early postpartum uterine disease (metritis) on the functional regeneration of endometrial glands in lactating dairy cows(University of Missouri--Columbia, 2024) Sellmer Ramos, Isabella; Lucy, Matthew[EMBARGOED UNTIL 12/01/2025] "The biological mechanisms that govern the establishment of mammalian pregnancy have been extensively investigated over the past century. Despite the advances, female fertility is continuously challenged by many intrinsic and extrinsic factors that are yet to be elucidated. A linear population increase is estimated to occur globally from the year 2000 to 2050 (Alexandratos et al., 2006). Unsurprisingly, these trends are expected to compel livestock production systems to accompany the growing demand for food, given that predictive metrics estimate that 68 percent and 57 percent of the global population will consume meat and milk, respectively, by the year of 2030 (Steinfeld and Gerber, 2010). The increasing populational demand for food poses a challenge for livestock producers across all food animal systems to maintain an efficient herd. The efficiency of livestock production systems typically relies on herd-level turnover rates as its single indicator; however, these only provide a broader picture of a variety of events that culminate into that single outcome. Given that, the demand for superior efficiency could be met by increasing the productive lifespan of production animals at an individual level, closely redirecting efforts towards the maintenance of consistent genetic progress alongside optimal health and reproduction (Vries, 2020). Currently, the productive lifespan of cattle destined to milk production remains suboptimal (? 3 lactations) in most large dairy systems across the United States, mostly due to the high incidence of health disorders and reproductive failure affecting lactating cows (Phuong et al., 2016; De Vries and Marcondes, 2020). A cascade of physiological, morphological, and metabolic adaptations during the transition from pregnancy to parturition and subsequent lactation create a significant challenge for dairy cows. Successful completion of early postpartum events is relevant to early postpartum milk production as well as optimal reproductive performance during the breeding period at later postpartum stages (Lucy, 2019; Sheldon et al., 2019). Amongst these events is the process of uterine involution, which is characterized by the functional reestablishment of the uterus to support subsequent pregnancies (Buch et al., 1955; Sheldon, 2004). Despite the success achieved by reproductive programs, fertility in lactating dairy cows remains suboptimal, with first service conception rates ranging between 30 percent to 40 percent (Fricke and Wiltbank, 2022; Sartori et al., 2023), mostly attributed to early lactation disorders that contribute to early embryonic loss (Ribeiro et al., 2016a; Wiltbank et al., 2016; Ribeiro and Carvalho, 2017). Amongst these disorders is metritis, an early postpartum uterine disease that affects approximately 25 to 40 percent of lactating dairy cows (Bromfield et al., 2015; LeBlanc, 2023; Bruinjé et al., 2024). Metritis is characterized by the presence of a red-brownish, watery and fetid uterine discharge, typically detected between 5-10 days postpartum (dpp) and often associated with clinical signs of systemic illness (e.g. pyrexia, cachexia and decreased milk production) (Sheldon et al., 2009) and other periparturient disorders (i.e. retention of fetal membranes; dystocia; vulvovaginal lacerations) (Vergara et al., 2014; Vieira-Neto et al., 2016). Caused by the dysbiosis of pathogenic bacteria within the postpartum uterus (i.e. Fusobacterium necrophorum; Bacteroides spp.; T. pyogenes), treatment options for cows diagnosed with metritis rely mostly on the administration of systemic antibiotic drugs (e.g. ceftiofur), which have been demonstrated to efficiently alleviate the systemic signs of infection (Galvão et al., 2019; Machado et al., 2020; Pinedo et al., 2020; Silva et al., 2023). Regardless of the significant rates of clinical cure associated to antibiotic treatment (Lima et al., 2014), the cost of metritis per case in the U.S. currently ranges from $156 to $948, and may vary based on treatment and fertility-related culling (Pérez-Báez et al., 2021), presenting a significant economic impact to the dairy industry, estimated at $1 billion per year. Failure to resolve bacterial infection and associated inflammation occurs in approximately half of the cows that are diagnosed with early postpartum metritis (Sheldon et al., 2020). Chronic bacterial infection results in the development of endometritis, a disease characterized by the presence of purulent content within the uterine lumen between 21 to 35 days in milk (DIM) and often associated with the presence of a purulent vaginal discharge (PVD), which may go undiagnosed and is greatly associated with the presence of pyogenic bacteria (e.g. T. pyogenes) (Sheldon et al., 2006; Pascottini et al., 2020). Microscopically, endometritis is characterized by an exacerbated innate immune response, evidenced by the presence of neutrophils and macrophages within the uterine lumen, frequently found infiltrated within the endometrial luminal epithelium (LE) and underlying stroma (stratum compactum) as well, in addition to the presence of lymphocytic foci (T and B cells) within the stratum compactum (Bonnett et al., 1993; Dadarwal et al., 2017). Early postpartum uterine disease is associated with a greater risk for pregnancy losses and a lengthened calving-to-conception interval, both often found to be correlated with a delayed resumption of cyclicity (i.e. ovulation) (Giuliodori et al., 2013b; a; Bruinjé et al., 2024). Despite the known association, the intrinsic mechanisms through which metritis and endometritis reduce fertility remain under investigated. A proposed mechanism for the association of uterine disease with poor fertility outcomes has recently emerged when researchers discovered that the outer membrane components of Gram-negative bacteria (lipopolysaccharide, LPS) are found within the follicular fluid of cows that experience early postpartum uterine disease further until 60 DIM, when cows are expected to undergo their first artificial insemination (Piersanti et al., 2019). Using an experimentally induced endometritis model in non-lactating dairy cows (i.e. T. pyogenes + E. coli), these studies demonstrated that bacterial induced inflammation impaired the developmental capacity of oocytes when fertilized in vitro (Dickson et al., 2020), and postulated that disease may impact fertility through a mechanism that disrupts ovarian homeostasis, and consequently, its germ cell pool. Nonetheless, the successful establishment of pregnancy extends past the phenomena of fertilization, requiring a functional endometrium that is permissive to the newly formed embryo. Following parturition, the uterus must undergo extensive remodeling in order to reestablish the endometrial histoarchitecture and cellular homeostasis prior to subsequent pregnancy attempts (Kiracofe, 1980; Salamonsen et al., 2021; Spooner et al., 2021). Accordingly, latest developments evidenced that experimentally induced endometrial inflammation (T. pyogenes + E. coli) in lactating dairy cows compromised the development of conceptuses as far as 16 days post- conception, suggesting that inflammation may compromise the embryotropic capacity of the endometrium during early lactation (Husnain et al., 2023). Given that, we hypothesized that early postpartum uterine disease may delay or permanently impact the reestablishment of a functional endometrial histoarchitecture, which could explain lower fertility in cows that experience early postpartum uterine disease. Given that a functional uterus is comprised of functional endometrial glands, which are essential for fertility (i.e. early embryonic development) (Spencer et al., 2019), we aimed to investigate the mechanisms through which uterine glands are reestablished at both physiological and pro-inflammatory conditions following parturition in lactating dairy cows."--Introduction.Item Inactivating members of the PAG gene family by utilizing cytdine deaminase CRISPR technology(University of Missouri--Columbia, 2024) Nelson, Benjamin; Green, Jonathan[EMBARGOED UNTIL 12/01/2025] Pregnancy-associated glycoproteins (PAGs) are aspartic proteinases produced by trophoblasts at the fetal-maternal interface. The exact functions of PAGs are unknown. This experiment aims to elucidate PAG function via the ablation of select porcine PAGs in embryos. PAG null embryos were generated via cytidine deaminase base editor. 2 guides targeting homology in 9 of the 12 PAGs were injected into zygotes via microinjection. Subsequent blastocysts were transferred to surrogates and then collected on various days of pregnancy (day 25, day 18). Day 25 yielded no pregnancies. On day 18, the conceptus was present, and PAGKO was confirmed. Histology showed aberrant vascular formation beneath the uterine epithelium. RNAseq analysis showed the down- regulation of several targets related to ECM remodeling. Porcine PAGs appear to affect proper ECM remodeling, though further research will be needed to elucidate the cellular mechanisms of these interactions.Item Exogenous donor-derived hepatogenesis in chimeric hosts(University of Missouri--Columbia, 2024) Yeddula, Sai Goutham Reddy; Telugu, Bhanu[EMBARGOED UNTIL 12/01/2025] This dissertation investigates advanced genetic engineering techniques and the creation of intra- and interspecies chimeras to explore liver development and the potential for generating donor-derived organs in chimeric hosts. In this dissertation, we begin with a comprehensive review of the literature (Chapter I) regarding histology and anatomy of liver, cardinal functions of the liver, followed by an overview of the current knowledge of embryonic liver development with a specific focus on molecular pathways and genes crucial for hepatogenesis. Specific focus was given to gatekeepr genes such as Foxa, Gata, and Hhex. We also highlight the role of Fah in maintaining liver homeostasis. Additionally, a generalized introduction to advanced genome editing techniques was provided. In Chapter II, we outlined optimized strategies for generating Hhex and Fah knockout embryos using CRISPR/Cas9 and base editing techniques. The outlined methods tested the latest genetic engineering techniques and demonstrated the feasibility of generating successful gene knockouts with improved precision and consistency. This establishes a foundation for creating reliable models to study organogenesis and embryonic development in the context of liver formation. In Chapter III, intra- and interspecies chimeras were then generated by using pluripotent stem cells and blastocyst complementation to assess the integration and functionality of donor-derived liver cells in the host embryos. Our findings reveal both the potential and limitations of intra and intererspecies chimerism in overcoming developmental barriers and achieving successful organogenesis. Building on these results, blastocyst complementation experiments were conducted in a large animal biomedical pig model lacking liver development (ahepatic pigs), successfully generating donor-derived liver tissues. Final Chapter was dedicated to summarize our current findings and a discussion on future directions to enhance the efficiency of generating exogenous organs. Taken together, this body of work is expected to advance our current understanding of the field of regenerative medicine by providing insights into the development of functional, donor-derived organs in chimeric hosts.