Veterinary Science - Theses
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ItemEffect of feeding slowly fermentable grains as protection against heat stress in ruminants( 2017)The combination of high environment temperatures, the heat increment resulting from feed fermentation and digestion (HI), high metabolic rates and metabolic heat production (HP) make ruminants susceptible to heat stress (HS). The reduction in the ratio forage-to-concentrate in the diet during HS is a traditional nutrition management aimed at increasing the energy content of the diet to compensate for reductions in dry matter intake (DMI) frequently observed in heat stressed ruminants. Wheat is a rapidly fermentable grain commonly used as an energy source for ruminants in Australia. However, the rapid rate of rumen starch fermentation of wheat is associated with rumen acidosis and elevated body temperature in cattle. By contrast, slowly fermentable grains, like corn, are associated with better utilization of metabolisable energy (ME) and reduced HI. Chemical treatment of wheat grains with sodium hydroxide (NaOH) or Bioprotect (BP) may reduce the rate of starch fermentation, HI and metabolic HP. The effect of feeding cereal grains differing in rumen fermentability on physiological, metabolic and productive responses of ruminants under high thermal load has not previously been evaluated. Therefore, it was hypothesised that by feeding slowly fermentable grains, the HI would be reduced, thereby reducing the effects of HS in ruminants. The research presented herein firstly investigated the differences between rapidly (barley and wheat) and slowly fermentable grains (corn, 3 % NaOH- and BP-treated wheat) on gas production kinetic parameters, pH, and starch and dry matter (DM) digestibility using in vitro experiments. Then, using in vivo experiments the effect of feeding either slowly or rapidly fermentable grain diets at different feed intake on HS related changes on physiological, metabolic and digestibility variables of wethers and the physiological, metabolic and productive responses of lactating dairy cows fed grain-based diets differing in grain fermentability during summer were investigated. In vitro experiments demonstrated the slower fermentability and higher pH during incubation of corn, BP- and 3 % NaOH-treated wheat compared with untreated wheat and barley. In vivo experiments demonstrated that HS induces changes in physiological variables, blood-acid base balance, and energy utilization in ruminants; that elevated DMI increases the thermal load of wethers under HS; that feeding wethers either a corn- or 3 % NaOH-treated wheat based diet, may increase the glucose available for intestinal absorption, can reduce the HI and ameliorates the physiological variables negatively affected by HS compared with untreated wheat; that the reduced total apparent starch digestibility of corn diets explains the improved responses observed in corn-diet fed wethers under HS condition; and that feeding 3 % NaOH-treated wheat improves apparent starch, DM digestibility, and DMI of wheat diet without increasing the metabolic HP. In the dairy cow experiment, a lower rectal temperature and higher milk yield was found in cows fed corn diets that were associated with reduced HI and metabolic HP, and higher glucose availability than in cows fed untreated wheat. It was also demonstrated that rumen temperature is a sensitive predictor of core body temperature and physiological and productive variables negatively affected by HS. Thus, this thesis demonstrated that the use of slowly fermentable grains is a viable nutrition management to improve thermo-tolerance of ruminants under high heat loads.
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ItemBacterial enteritis in young Merino sheep.( 2017)Diarrhoea during winter is a common problem of sheep in the high rainfall regions of south-eastern Australia. Gastrointestinal nematodes are the primary cause of this problem, especially in young Merino sheep (those <16 months old). However, a syndrome of persistent diarrhoea (‘winter scouring’) is also relatively common in young sheep with low or moderate nematode burdens, with outbreaks usually occurring between June and October. Affected animals have profuse, watery diarrhoea, and often show signs of abdominal discomfort. Before this study, the cause of this syndrome and the epidemiology and risk factors for outbreaks and faecal shedding of the causative organisms, were not well understood. To determine the primary cause of the syndrome, 45 outbreaks of ‘winter scouring’ were investigated on 24 farms across south-eastern Australia. Necropsies were conducted and faecal samples were collected from animals in affected flocks. Faecal and tissue samples were cultured for Yersinia, Salmonella and Campylobacter species, and faecal WECs conducted to assess nematode parasitism. The sensitivity of Yersinia isolates to four common antimicrobial compounds was also assessed. Yersinia pseudotuberculosis serotype III and virulent Y. enterocolitica were the most frequently isolated bacteria, with outbreaks typically occurring when more than 10% of the mob were shedding either of these organisms. Campylobacter and Salmonella did not play a role in any of the outbreaks investigated. Over 64% of all Yersinia isolates were resistant to sulphonamides, but 98% were susceptible to oxytetracycline. These results highlighted the need to investigate the epidemiology and risk factors of yersiniosis in more detail to support the development of more effective control strategies. As a first stage of this process, a longitudinal study was conducted on four farms to evaluate the patterns of faecal shedding of Yersinia and assess some potential risk factors for outbreaks of yersiniosis, including live-weight, average daily weight gain and WEC. Faecal shedding of both species occurred predominantly during the winter, but shedding of Y. enterocolitica also occurred at other times. Therefore, in addition to scouring in winter, Y. enterocolitica can also cause diarrhoea at other times. In contrast to the outbreak investigations, the prevalence of faecal shedding of Yersinia species was often very high (>30% of animals within a mob) without any clinical disease. This suggests that complex interactions between risk factors contribute to yersiniosis, and that simply monitoring the prevalence of faecal shedding of Yersinia species will not be a reliable predictor of an outbreak of yersiniosis. High WECs (>300 eggs per gram) were associated with an increased risk of shedding each Yersinia species, and so effectively controlling gastrointestinal nematodes should also decrease the risk of yersiniosis. Animals that gained weight were less likely to shed Y. enterocolitica, but more likely to shed Y. pseudotuberculosis. Despite this, the current strategy of ensuring weaner sheep (those 3-12 month of age) continue to gain weight during autumn and winter is still recommended. The effect of an autogenous bacterin against Y. pseudotuberculosis serotype III was assessed on two farms that consistently had severe outbreaks of yersiniosis. There was no outbreak in the year of the study (2014), and vaccinated weaners had similar live weight, growth, faecal shedding of both Yersinia spp. and antibody titres to Yersinia outer membrane proteins to unvaccinated controls. Consequently, further studies to evaluate the efficacy of vaccines during an outbreak of yersiniosis are required.
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ItemImpacts of heat stress on the biomarkers of oxidative stress in sheep and potential nutritional strategies for amelioration( 2015)Heat stress (HS) is a multi-billion dollar global problem as it impairs animal performance during the summer. Heat stress has been implicated in promoting oxidative stress either through excessive production of reactive oxygen species (ROS) or decreased antioxidant defence. Excessive ROS production overwhelms the antioxidant defence, and this leads to oxidative damage of biological molecules including proteins, lipids and DNA, which in turn disrupts normal metabolism and physiology. Therefore, a robust antioxidant network capable of preventing oxidative damage of biological molecules holds promise for improving the health and performance of animals during heat stress. This thesis investigated the impacts of heat stress on the oxidative stress biomarkers, elucidated potential role and optimized the dose of vitamin E and selenium required to ameliorate heat stress in sheep. The first study investigated the impact of HS and dietary antioxidant supplementation on the oxidative and physiological status of sheep. This study showed that heat stress negatively affects the oxidative status of sheep along with the physiological responses; however some of these affects can be ameliorated through dietary vitamin E (Vit E) and selenium(Se) supplementation at supranutritional concentrations. To understand the molecular mechanisms involved in heat stress ameliorative action of Vit E and Se, mRNA expression of heat shock proteins (HSP) and pro-inflammatory genes were investigated. High dietary antioxidants proved to modulate skeletal muscle expression of HSP, pro-inflammatory cytokine and NFĸB transcription factor, which may protect against HS in sheep. The potential role of high dietary Vit E or Se in amelioration of HS in sheep, and changes in acid base balance and respiratory oxidative stress biomarkers along with systemic biomarkers, were investigated in the second study. This study suggested that the hydrogen peroxide concentration in exhaled breath condensate (EBC) can be utilized as a novel biomarker to demonstrate respiratory oxidative stress induced by HS in sheep. The study also highlighted the potential of Se to reduce respiratory oxidative stress. While Vit E improved the physiological responses of heat stressed sheep; combined supplementation of Vit E and Se was required to prevent the acid base imbalance in heat stressed sheep. Finally, optimization of dietary levels of Vit E and Se to improve the performance and oxidative status of lambs finished during hot conditions was undertaken. This study suggested that supranutritional levels of dietary Vit E and Se increased average daily feed intake and the average daily gain in lambs during finishing and maintained the oxidative balance during exposure to HS. Thus it is suggested that heat stress leads to oxidative stress in sheep and supranutritional supplementation of dietary Vit E and Se can be used as a nutritional strategy to ameliorate negative effects of HS in sheep. Further research is required to elucidate the effects of dietary Vit E and Se on retail colour stability and shelf life of meat obtained from lambs finished under hot conditions.
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ItemThe therapeutic use of mesenchymal precursor cells in an ovine collagen induced arthritis model of rheumatoid arthritis( 2013)Rheumatoid arthritis (RA) is an autoimmune disease that affects 1% of the population and causes joint destruction, deformity and substantial disability. The current treatment of the disease alleviates the clinical symptoms to some extent but does not affect a cure. Also, the patient’s response to current therapeutic options is highly variable and often incomplete, reflecting the complex involvement of multiple pathways in RA disease progression. Furthermore, continuing anti-inflammatory treatment may suppress immune responses essential in host defense. Thus, despite current therapies, novel therapeutic approaches to RA are required. Mesenchymal stem cells (MSC) are self renewable, multipotent, non-hematopoietic progenitor cells that have the capacity to differentiate into various lineages like adipocytes, osteocytes and chondrocytes. Additionally, they have immunomodulatory properties that are considered as a potential therapy for immune mediated diseases and for RA in particular. To examine the therapeutic effect of these cells, animal models that can mimic the human disease are required in order to investigate the immunomodulatory effects of these cells. Collagen induced arthritis (CIA) is the most studied and used RA model in animals, as it shares many pathological and immunological features of the human disease. Although CIA has been examined in a number of species including mice, rats and monkeys, it has not been fully investigated in a large animal model that might offer more advantages over the current rodent models and which may more closely resemble humans in joint size and degree of load bearing. The aims of this study were first to develop the CIA model of RA in sheep and confirm its reproducibility and capacity to provide efficient assessment of disease activity before investigating the efficacy of allogeneic ovine mesenchymal precursor cells (MPC) which had been immune-selected and culture-expanded to reduce arthritis in this model. MPC are a later developmental stage of MSC and because of their purification techniques through the isolation using stro1 and stro3 antibodies, they are more homogeneous population of cells than MSC. Two subcutaneous (s.c.) injection of bovine collagen type II (BCII) in freund’s adjuvants followed with intra-articular (i.a.) injection of the same protein in saline in the hock joints has resulted in establishment of CIA in sheep with arthropathy displaying much of the classical pathology associated with human RA. Further, it provided clinical, histopathological and immunopathological features that can be used in testing biological therapeutics for the treatment of RA, such as stem cells. Following induction of arthritis with collagen, clinical signs of lameness and swelling were evident in all sheep and gross thickening of the synovium surrounding the hock joint and erosion on the cartilage surface was evident at necropsy (2 week and 6 week time points). Leukocyte cell counts and levels of antibodies to BCII were increased in serum and synovial fluid (SF), and there was synovial hyperplasia, thickening of the intimal layer, inflammation and marked angiogenesis in the synovial tissue. There was a large influx of monocytes and both T and B lymphocytes to the synovial tissue, many of which appeared to be in active phases of their cell cycle. After CIA establishment in sheep, the therapeutic effects of allogeneic ovine MPC were investigated in the early stages of CIA by Intravenous (i.v.) administration of MPC one day after arthritis induction. The development of arthritis was followed for two weeks before the sheep were euthanized. Sheep in the MPC treated group showed significantly reduced clinical signs throughout the trial and also showed significant reductions in the pro-inflammatory markers, IL-6 and acute phase proteins (APP) in blood. Activin A levels in both blood and SF of the treated group were also significantly lower than in the control group. Conversely, blood levels of the anti-inflammatory cytokine IL-10 showed a large spike following the administration of MPC. MPC treatment also lowered the neutrophil response in blood following arthritis induction, and the influx of CD4+ cells and monocytes into synovial tissues. All of these effects were accompanied by a significant reduction in the severity of histopathology in the synovial membranes of the treated hock joints compared to the control ones. These results indicate that the immunomodulatory features of MPC have a dramatic effect on acute inflammatory processes involved in arthritis and could become a first line treatment for reducing inflammation and destruction in the joints of people suffering from severe RA. The second MPC study in this thesis was to investigate the effects of MPC on later stages of arthritis using three different MPC doses and with i.v. and i.a. routes of administration. MPC were administered two weeks after arthritis induction and the sheep were monitored for four weeks. In the control sheep, histopathological analysis of hock joints demonstrated that the left hock synovium was characterized by leukocyte infiltration, synovial hyperplasia, pro-inflammatory cytokine expression, and cartilage erosion. In comparison with saline treated controls, synovial tissue from arthritic sheep receiving a single i.v. injection of MPC showed reduced histopathology scores and reductions in the expression of the pro-inflammatory cytokines IL-6, TNF-α, and IL-17 and absence of IL-1β expression. This was accompanied by a significant reduction in infiltrating monocytes/macrophages and a slight increase in the levels of the anti-inflammatory cytokine IL-10. The i.a delivery of MPC did not appear to lessen the intensity of the arthritis. These results indicate that a single i.v. injection of MPCs in an ovine model of collagen-induced RA attenuates joint inflammation, involving inhibition of the Th17 T cell subset and monocyte-derived production of multiple pro-inflammatory cytokines. Together, these data suggest that MPCs may have great potential as a first line treatment for joint inflammation and RA disease progression.