School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEffect of Irrigation, Glycine Betaine and Kaolin Particle Film on the Performance of Vitis Vinifera L. ‘Shiraz’( 2019)Environmental stresses, such as heat and water stress, are a current and emerging challenge to wine grape production in Australia. In Southern Australia, where wine grape production is predominately located, Global Circulation Models (GCMs) predict further increases in temperatures, increased frequency and severity of heatwaves and reduced rainfall. Wine grapes are particularly susceptible to heat and water stress due to the lengthy grapevine establishment times and the perennial nature of this crop. Therefore, there is a strong demand for management strategies to protect established vineyards from environmental stresses, such as heat and water stress. Glycine betaine (GB) and kaolin particle film (KPF) are two products that can be exogenously applied to grapevines to potentially ameliorate the effects of heat and water stress. The objective of both foliar sprays is the same, but their mode of action is quite different. GB seeks to induce greater stress tolerance, while KPF seeks to physically protect the fruit and leaves. Management strategies, such as application of GB and KPF, implemented to ameliorate the effects of one stress may however have unintentional impacts when coupled with common management practices, such as deficit irrigation. This research investigated the protective capacity of GB and KPF, individually and combined, on grapevine performance under varying levels of imposed water stress, and their associated interactions on the productive performance and physiology of Vitis vinifera L. ‘Shiraz’. A field experiment was conducted on Shiraz (clone SA16) vines at The University of Melbourne’s Dookie Campus Vineyard in North East Victoria, Australia during the 2011-12 (Y1) and 2012-13 (Y2) growing seasons. The vines were planted in 1994, on Richter 99 rootstock on a cordon-trained Scott Henry trellis system, with two bilateral cordons. A randomised complete block design (RCBD) factorial experiment was established in 2011 comprising three irrigation treatments, two GB treatments and two KPF treatments, with six replicates per treatment. Analysis was conducted on grape yield and yield components, fruit composition, plant water status, canopy growth and canopy temperature. The research was conducted over two contrasting growing seasons. Y1 was largely cooler with high rainfall between veraison and harvest and Y2 was hotter with lower rainfall. In Y2, observed values of leaf water potential and canopy temperatures indicated that all the treatments were showing signs of severe to very severe water stress. Consequently, water availability (rainfall and irrigation) dominated treatment responses in yield and composition, with average berry weight across all treatments 52% smaller, resulting in a 25% lower average yield in Y2 compared with Y1. Therefore, seasonal variation played a key role in the vines’ response to the irrigation treatments, GB and KPF. Under non-stressed conditions in Y1, applying GB resulted in a 16% reduction in grape yield, which was attributed in part to an 8% reduction in berry weight. However, under severe water stressed conditions in Y2 the impacts of GB on vine performance became less evident. Applying KPF resulted in a reduction in some yield components under the water stressed conditions of Y2. It is possible that KPF resulted in changes to transpiration resulting in the vines becoming more water stressed. In addition, the interaction of GB and KPF may have caused a response similar to the effect of KPF under water stressed conditions. This is evidenced by the combined effect of GB and KPF resulting in lower average cluster weight in Y1 and more negative values of midday leaf water potential post-irrigation in Y2. However, interpretation of this interaction is complicated by the impacts of the irrigation treatments and seasonality. In conclusion, this research has shown how Shiraz vines respond to GB and KPF, when grown in commercial settings, under both high and low water availability conditions in North East Victoria, Australia. These findings are important as they indicate that the use of these compounds to ameliorate the impacts of environmental stresses, such as heat stress, needs to be carefully assessed alongside water availability. Importantly, these research findings have demonstrated that GB and KPF have different impacts across different environmental conditions; and there is a potential for interactions that could compromise production of grapes to meet commercial specifications.
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ItemThe physiology and functional genomics of the heat stress response in dairy cattle( 2017)Thermal stress experienced by dairy cattle, can be one of the greatest limitations on production efficiency and animal health. In the Australian climate the effects of heat stress causes millions of dollars in lost production every year. A correlated response to selection for improved milk production has facilitated an increase in metabolic heat and susceptibility to thermal stress. With the increase in the frequency and severity of heat events in the temperate climate dairying regions of Australia, the need to identify and breed heat tolerant dairy cattle is one of the most important traits. New information regarding the physiological responses to heat stress, will assist in determining the heat stress susceptibility of dairy cows in the Australian climates and reinforce the need to employ amelioration strategies. Amelioration strategies for heat stress in the Australian dairy industry, are often limited by the fact that the majority of dairy cows are exposed to the elements as they graze pasture. Techniques such as providing shade, sprinklers and fans becomes challenging and expensive for the producers. Another, perhaps more practical amelioration strategy is the identification of genetically heat tolerant dairy cows. The research presented in this thesis firstly examines the physiological and metabolic responses of Australian dairy cows to experimentally induced heat stress which replicates the moderate short-term heat events observed in the temperate climates of Australia. The experiment presented demonstrates the susceptibility to heat stress of dairy cows which are adapted to a temperate climate. The experiment also described the recovery period after exposure to a heat challenge, which identified that there was a delay between the return to normal feed intake and milk production. This indicates that there may be a period of metabolic recovery required post heat exposure. This thesis also presents an experiment validating genomic selection for heat tolerance within the Holstein Friesian breed. Genome wide DNA marker based prediction (genomic predictions) of heat tolerance from previous research were validated, as the genomically predicted heat tolerant cows during experimentally induced heat stress maintained milk production and feed intake to a higher level, and had lower core body temperature than genomically heat susceptible cows. The experiment also found that there are thermoregulatory differences between genomically heat tolerant and heat susceptible cows, as the heat tolerant cows displayed more efficient heat dissipation mechanisms via evaporative cooling. This validation of genomic selection technology is an important progression towards breeding heat tolerant dairy cows in the future. The cellular changes at the molecular level in response to heat stress were investigated using global gene expression changes derived from whole transcriptome mRNA sequencing. The thesis presents global gene expression changes in vivo in white blood cells and milk cells of dairy cows experiencing experimentally induced heat stress. This experiment identified that there is a verifiable link between the heat stress phenotypes and gene expression. The genes identified to be differentially expressed in the blood, suggest that fatty acid metabolism, immune responses, inflammation, and blood pressure regulation were affected by heat stress. The transcripts in the milk suggest that cholesterol metabolism and lipolysis, and antibody production were also impacted by the heat challenge. These findings provide new insights into molecular adaptations induced during moderate short-term heat stress. Novel differences in global gene expression changes in vivo in the blood of genomically selected heat tolerant and heat susceptible cows were identified. The genes differentially expressed between heat tolerant and heat susceptible cows, suggest that lactation, glycolysis, lipid metabolism and oxidative stress related gene regulation was affected differently in the heat tolerant cows compared to the heat susceptible cows. This investigation of the functional genomic responses in the white blood cells during heat stress demonstrated the depth of the cellular response to heat. Biological pathways that were consistently affected by heat stress throughout the thesis were lipid metabolism, carbohydrate metabolism, apoptosis and protein folding, and a candidate list of genes were identified for further targeted research.
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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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ItemEnvironmental factors influencing flower development and accumulation of pyrethrins in pyrethrum( 2016)Pyrethrum is commercially grown for extraction of pyrethrins which accumulate in the achenes of the flowers and are used as a natural insecticide. In Chapter 1, the literature review indicated that there were gaps in knowledge, especially concerning the effects of environmental stresses on flower development and accumulation of pyrethrins. Variability in yield of pyrethrins from season to season was identified as a significant problem for the pyrethrum industry in Australia. Water deficit and heat stress were considered to be the major environmental factors influencing flower development and accumulation of pyrethrins in pyrethrum and detailed glasshouse and field experiments were conducted to better characterise the responses of this perennial crop to these stresses. In Chapter 2, investigation of the pattern of accumulation of pyrethrins, achene and trichome development in relation to the pattern of flower development showed that flower size, achene number and size, trichome number, rate of flower maturity, duration of flowering period and rate of accumulation of pyrethrins significantly correlated with final yield of pyrethrins per flower. In Chapters 3 and 4, exposure of plants to short periods of heat stress and water deficit during the flowering period caused a significant reduction in the flower, achene and pyrethrin yield due to a reduction in flower size and accelerated flower senescence. Exposure of pyrethrum plants to heat stress and water deficit also significantly increased the rate of flower development resulting in a shorter flowering period and a slower rate of accumulation of pyrethrins. Overall, adequate soil moisture and optimum temperature for flower development increased both the rate and duration of pyrethrin accumulation and greatly increased the yield of pyrethrins per flower. Timing and duration of heat stress and water deficit significantly influenced pyrethrin yield per flower. Heat stress and water deficit caused more severe yield reductions at early flowering than later in the flowering period. In Chapter 4, deep rooting was identified as an important factor in alleviating the negative effects of moderate water deficit and minimizing yield reductions. In Chapter 5, irrigation of pyrethrum increased both the rate and duration of pyrethrin accumulation and greatly increased the yield of pyrethrins per flower. Overall, the impact of irrigation on pyrethrum yield depended on timing and duration of application. Irrigation applied at the early and mid-flowering stages increased flower number whereas irrigation applied at mid and late-flowering stages increased flower size. Based on all the investigated irrigation treatments, irrigation applied at both early and mid-flowering stages was the most efficient and economical irrigation management strategy for this crop. In Chapter 6, elevated atmospheric carbon dioxide throughout the flowering period increased flower yield and yield of pyrethrins per plant due to the production of more flowers. The interaction of water deficit with elevated atmospheric CO2 increased the rate of flower development resulting in shorter flowering period. Plants grown under elevated CO2 had increased rooting depth, root length and root biomass which minimized the negative effect of moderate water deficit on pyrethrum yield through greater water uptake from deeper soil layers. In conclusion, a perennial crop like pyrethrum producing economically valuable secondary metabolites appears to be well-suited for future farming systems. Deep rooting and tolerance of moderate water deficit and heat stress, together with good responsiveness to elevated CO2, should allow the crop to yield well under predicted climate change.
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ItemNutritional strategies to alleviate heat stress in pigs( 2016)Heat stress (HS) is a production, welfare and health issue during summer. With the impacts of climate change forecast to increase global temperatures, increasing participation in tropical agriculture and selection for more productive genotypes, HS is both a current and emerging problem. Heat stress compromises efficient pig production by diverting energy from optimal pathways for growth, lactation and reproduction. Strategies to ameliorate HS in production pigs include engineering controls such as improved ventilation, shade and misting sprays as well as adjusting the macronutrient formulation of the diet. However, there is increasing evidence that development of low cost micronutrient additives can be of great benefit to production animals experiencing HS. The objective of this thesis was to investigate micronutrient additives as a means of ameliorating the impacts of HS on pig physiology. The application of this knowledge will be to augment existing strategies, reduce seasonal variation in production, improve productivity in tropical environments and provide an adaptation strategy against climate change. The main impacts of HS include the reduced feed intake, altered physiology, impaired intestinal barrier function, and altered insulin-related metabolism, and these impacts may be partially related with increased oxidative stress. Macronutrient modification is one management strategy however there is emerging evidence for the benefits of micronutrient formulations such as selenium (Se), vitamin E (VE), chromium (Cr) and betaine (Chapter 2). The unified hypothesis tested in this thesis was that supplementations with the functional nutrients (Se, VE, Cr, betaine) above the current NRC recommendations can mitigate impacts of HS in pigs. Methodology was stated in the Chapter 3, and briefly in each experimental chapter. As oxidative stress may be associated with various impacts of HS such as hyperinsulinemia and increased adiposity, the effects of supranutritional Se (1.0 ppm) and VE (200IU/kg) supplementation on oxidative stress markers as well as physiological response to HS were separately quantified in Chapters 4 and 5. The outcomes of the experiment in Chapter 4 showed that HS increased oxidative stress and reduced lipid mobilization independently of insulin concentrations. Supranutritional Se reduced hyperthermia, as indicated by reductions in rectal temperature compared to control, and VE ameliorated respiratory alkalosis in the heat-stressed pigs, indicating improved tolerance to HS. However, neither the Se or VE supplementation reduced markers of oxidative stress. As VE and Se differ in their biological function, with VE being rapidly absorbed into tissue and distributed into cell membranes where it prevents lipid peroxidation. Alternatively, Se is incorporated into newly synthesized proteins, where it contributes to a high capacity enzymatic route of elimination for free radicals. As HS was demonstrated to increase oxidative stress in Chapters 4 and 5, it was proposed that a combination of VE and Se would be more effective than either nutrient in isolation. Therefore, in Chapter 6 the influence of Se and VE combined supplementation was investigated on intestinal epithelial barrier integrity, a known site of oxidative damage during HS. This experiment confirmed that HS induced oxidative damage which in turn induced mucosal damage, as indicated by increased permeability. Addition of supranutrtional concentration of Se and VE reduced oxidative stress and protected against intestinal damage. This result was then further confirmed using a cell culture model of the porcine jejunum. Radiant heat loss is one of the primary heat dissipation measures by the pig and occurs by redistributing blood flow from the core to the periphery. The result is that visceral organs such as the intestines have insufficient blood flow and can result in tissue hypoxia and oxidative stress, compromising mucosal barrier function. Utilizing the non-transformed porcine jejunum cells (IPEC-J2), it was demonstrated that the effects of oxidative stress (Chapter 8) and hypoxia (Chapter 7) were more damaging than the direct effects of increased temperature (Chapter 7). Furthermore, consistent with its antioxidant function, Se mitigated the damage induced by oxidative but not hypoxic stress on barrier integrity of IPEC-J2 monolayers (Chapter 8). Improving insulin sensitivity may increase skin blood flow and facilitate heat dissipation during HS conditions, however, antioxidant supplementation did not improve insulin sensitivity as observed in the HS conditions (Chapters 4), therefore the effect of supplementation with a known insulin sensitizer, Cr (400 ppb in the form of chromium picolinate), was investigated in Chapter 9. Chromium augments insulin sensitivity when incorporated into the protein chromodulin, which augments insulin receptor binding. The results indicated that Cr improved insulin sensitivity. Furthermore, Cr fed pigs were more heat tolerant, as evidenced by lowered body temperature and respiration rate. The experiments conducted up this point had been under climatic controlled settings. To demonstrate application to production settings in the final experiment a standard NRC diet was reformulated to include Se, VE, Cr and betaine at levels identified through our previous investigations in lactating sows, which are highly susceptible to HS, during a typical summer at a commercial piggery (Chapter 10). The post-partum period is marked by substantial weight loss in sows as they divert energy from lactation. The primary result of the experiment was that sows on the experimental diet experienced a lesser degree of weight loss than control sows, indicating an improved tolerance to summer production and is expected to help producers counter seasonal production losses. The unified hypothesis tested in this thesis was that supplementations with the functional nutrients (Se, VE, Cr, betaine) above the current NRC recommendations can mitigate the negative impacts of HS in pigs. Taken together, the unified hypothesis of this thesis is accepted that the nutritional supplementation such as Se, VE, Cr and betaine above the current NRC recommendations can mitigate the impacts of HS in pigs.
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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.