School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemResource selection of small mammals in post-fire environments( 2022)Fire is an important ecological driver and widely used land management tool that alters habitats across the globe. Animals are often most affected by fire indirectly through its effects on resources. However, the interrelationship between fire, resources and animals is complicated as these phenomena interact at various spatial and temporal scales. This thesis aims to determine the influence of fire, environmental gradients and habitat and food resources on small mammals. I used complementary approaches to achieve this: I investigated occurrence, diet and resource selection, and studied this at multiple spatial scales. An introduction, three data chapters, and a synthesis make up my thesis; summaries of each data chapter are as follows. In Chapter 2, I investigated the influence of post-fire age, environmental gradients and resources on the occurrence of small mammals. Elliott trapping and habitat surveys were carried out, and Generalised Linear Models (GLMs) were used in analysing the relationship between the variables across different spatial scales. Habitat resources better predicted small mammal occurrence than time since fire or food availability (invertebrate biomass). Strong environmental gradients and the weak relationships between fire and resources likely drove the lack of fire responses. This chapter highlights the importance of habitat resources in facilitating species persistence in fire-prone landscapes. In Chapter 3, I investigated the diets of small mammals and how the diets changed over time after fire. I analysed small mammal scat using eDNA metabarcoding technology to obtain high-resolution taxonomic information. The results showed a diverse array of small mammal diet items, and overall diets were different for each species. I found out that the diet of one predominantly insectivore focal species (yellow-footed antechinus, Antechinus flavipes) also included substantial amounts of plant matter. Overall, the diets of the three focal species changed to different degrees with respect to different post-fire growth stages. This chapter provides insights into the dietary requirements of three native mammal species and changes in resource use over time after a fire, guiding land managers to reduce fire impacts on small mammals across the landscape. In Chapter 4, I investigated the resources selected by yellow-footed antechinus in foraging events within their home ranges. Individuals were radio tracked and foraging locations compared to random locations in the landscape. Findings suggest that individuals selected locations with denser vegetation for foraging, potentially as a predator avoidance strategy. Further studies, such as experimental manipulations are required to determine how study species use structural resources depending on changes in vegetation cover caused by disturbances such as fires. An understanding of the different resource requirements of animals is essential for developing successful conservation and land management plans. This thesis emphasizes the importance of acquiring comprehensive ecological information on species resource selection, especially the importance of diet and dietary resources. This thesis highlights the importance of using complimentary approaches such as live trapping, radio tracking and novel eDNA metabarcoding to understand interrelationships between resources and small mammals in post-fire environments at multiple scales. The approaches and findings of this thesis can guide conservation actions in post-fire environments.
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ItemAmelioration of the effects of heat stress with antioxidant enzymes superoxide dismutase and catalase in broiler chickens( 2022)Heat stress has become a growing concern in the livestock industry. Elevated temperatures, coupled with rising global animal production is severely impacting animal health, welfare and overall production capacity. Heat stress is associated with a myriad of physiological, metabolic and gastrointestinal changes and has been shown to induce oxidative stress, a condition in which harmful free radicals are produced in excess. Oxidative stress is particularly damaging to macromolecules and causes widespread cell and tissue damage. Emerging research suggests supplementation with antioxidants, such as Vitamin C and Vitamin E, can partially ameliorate the damaging effects of heat stress. Despite considerable research on antioxidant supplementation in livestock, there has been little investigation into the therapeutic effects of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). Therefore, the aims were to determine the effect of both antioxidants and antioxidant enzymes on growth parameters, meat quality, gastrointestinal health and markers of oxidative stress in heat stressed broiler chickens.
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ItemClimate and climate change effects on carbon uptake and storage in Australia’s wooded ecosystems( 2022)Forest ecosystems are central to the land carbon sector due to their capacity to store and sequester carbon. Many studies have demonstrated that forest carbon uptake and storage is strongly dependent upon climatic conditions. However, the effects of climate on forest carbon uptake and storage in different biomes are still uncertain. Climate change may alter carbon dynamics within forest ecosystems through the direct effects of increased temperature, increased CO2 concentration and changing precipitation regimes. Yet forests may also adjust to changing climate through mechanisms such as thermal acclimation. In this thesis I used three modelling approaches (machine learning, boundary-line analysis, and a land-surface model) to examine how climate of the recent past, present, and future affect carbon uptake (as Gross Primary Productivity, GPP) and storage (as above-ground biomass, AGB) in Australian forests. Furthermore, I explored how current GPP adjusted to thermal regimes and how acclimation affected carbon uptake and storage in the future. In my first quantitative chapter (Chapter 2), I explored relationships between carbon storage (as AGB) with climate and soil in Australian forests across the continent. I developed RandomForest models with climate-only, soil-only, or climate plus soil variables to examine whether climate or soils are better predictors of forest biomass at the continental scale and to identify the most important predictor variables. In this chapter I demonstrated that climate (particularly temperature and the timing of precipitation) was more important than soil for explaining variation in AGB across Australia’s forests. In Chapter 3, I used boundary-line analysis to examine the ecosystem temperature response of carbon uptake (as GPP) in 17 wooded ecosystems representing five distinct ecoregions. These responses were represented as a convex parabolic curve that was similar in shape among ecoregions – narrow in tropical forests and broader in woodlands. I then derived the thermal optima of GPP (Topt) from these curves for each ecosystem and examined the relationship between Topt and mean air temperatures across sites. My analysis revealed a strong positive linear relationship between Topt and mean air temperature that indicated GPP was optimised to the present climate. Finally, in Chapter 4, I predicted how carbon uptake and storage will be affected by climate change in these 17 ecosystems and examined the effects of thermal acclimation of photosynthesis on these predictions. I used the CABLE-POP land surface model adapted with thermal acclimation of photosynthetic functions and forced with climate projections from the extreme climate scenario RCP8.5. My simulations indicated that increased temperature, CO2 concentration and changed precipitation patterns will have a positive effect on future carbon uptake and storage in the majority of the 17 ecosystems. Furthermore, thermal acclimation of photosynthesis is likely to enhance this effect in tropical ecosystems. My results confirm that carbon uptake and storage in Australian forests are fundamentally linked to temperature and precipitation regimes, and that these forests may be capable of adjusting to climatic conditions. My research indicates that the direct effects of climate change are likely to enhance the storage and sink capacity of Australia’s forests in the future. While I did not assess the indirect effects of climate change on carbon cycles through changes to disturbance regimes, overall, my thesis suggests that carbon uptake and above-ground biomass carbon stores in Australia’s forests are likely to be resilient to climate change.
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ItemLeaves to landscapes: what drives litter bed flammability?( 2022)Fire is an important disturbance globally, shaping the structure and composition of many forested ecosystems. While fire is a natural process, large, extreme fire events can have devastating consequences on people and the environment. Predicting when and where fires occur is key to being able to manage these impacts. Most forest fires start as small fires, igniting and initially spreading in the litter bed – the layer of dead leaves, twigs and bark on the forest floor. Despite the importance of litter beds to wildfire occurrence and intensity, our understanding of the drivers of litter bed flammability remains incomplete. Thus, the over-arching aim of this thesis was to examine the drivers of litter bed properties and flammability, in order to better understand the mechanisms underpinning litter bed flammability. Starting at the leaf-scale, I reviewed the literature on leaf traits, litter structure and flammability to summarise current knowledge and identify knowledge gaps (Chapter 2). I performed a meta-analysis using existing data collated from key laboratory flammability studies in different fire-prone biomes. Leaf traits predominately influenced flammability indirectly, via litter structure. The packing ratio and bulk density of the litter bed were influenced by different combinations of leaf traits and, in turn, they aligned with different flammability metrics. Importantly, the effects of the leaf and litter traits were consistent across a wide range of taxa and biomes. However, uncertainty remained regarding whether the relationships identified in simple litter beds continue to be important at field-scales in litter beds which are more complex in relation to their structure, composition, and moisture content. Hence, I developed and tested the effectiveness of a laboratory method to measure ignitability of litter beds collected from the field (Chapter 3). I examined how the results of this laboratory method matched a similar but more logistically complex field method, to better understand the scalability of laboratory experiments. I found that laboratory experiments can be adequate surrogates for field experiments, particularly under low wind conditions and where there is little near-surface fuel and litter beds are the dominant receiving fuel for firebrands. I used this laboratory method to examine how flammability varies as a function of moisture, in combination with other factors, at two spatial scales: the litter bed and the vegetation community, sampling forested sites along an aridity gradient (Chapter 4). At the litter bed-scale, moisture content was a key predictor of ignition and flame spread rate. Moisture thresholds varied with leaf cover for ignition and leaf size for flame spread rate. Conversely, bulk density was a key predictor of flame duration, not moisture. At the community-scale, Vapour Pressure Deficit (VPD) was the best predictor of site-level ignitability. Aridity shaped the relationship between VPD and ignitability, reflecting differences in canopy cover and its influence on forest microclimate and fuel moisture dynamics. Less arid parts of the landscape had a higher VPD-threshold for ignition than more arid parts, meaning they are available to burn less often. Finally, I considered how management actions influence litter beds and understorey fuel (Chapter 5). Using data from a long-term ecological burning experiment, I examined how frequent prescribed burning and timber harvesting influenced the amount and composition of fine fuel, and the implications for flammability. Frequent fire had consistent effects irrespective of harvesting, increasing the amount of leaves in the litter bed and decreasing the amount of live understorey fuel. Overall, this research provides insight into the mechanisms underpinning litter bed flammability, from leaves to vegetation communities. This information can be used to improve fire prediction and fuel management.
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ItemFrom Cruelty to Care: informing human behaviour change interventions to improve dog welfare( 2022)From cruelty and neglect to mismanagement and suboptimal care, the primary cause of most dog welfare problems is owner behaviour. Consequently, owner behaviour change is likely the most promising avenue for improving the lives of companion dogs. Behaviour change as a scientific discipline is well-established in other fields such as health psychology, but has had limited systematic work in animal welfare settings. Previous animal-related interventions have largely lacked appropriate foundational research to understand the nature of the chosen problem and appropriate targets for interventions, including target audiences and target antecedents of the relevant behaviours. Consequently, the aim of this thesis was to contribute to the evidence base regarding dog welfare problems and owner behaviour to inform future intervention development. The thesis examines both ends of the ‘dog welfare spectrum’, from animal cruelty and neglect, through to appropriate care and management, to present a broader understanding of the topic. The first study provides novel insights about the prevalence and nature of cruelty and neglect at the community level. Using a representative telephone survey it demonstrated that mistreatment is common, underreported, and mostly neglect. Additionally, it showed that rates of community reports made to authorities are not accurate indicators of mistreatment prevalence within a given region and should not be relied upon for selecting intervention target audiences. Finally, a higher prevalence of mistreatment was identified in the regional cities surveyed compared to the metropolitan and interface regions. This was likely attributable to socioeconomic challenges. The second study built upon the first by evaluating community attitudes towards animals and their treatment as potential targets for interventions. Specifically, it examined whether the prevalence and reporting trends found in the first study were reflected in community attitudes. While small differences were found that reflected these trends, overarchingly the study demonstrated the complexity of community attitudes. This complexity highlights the need for clear identification and understanding of an intervention’s target audience. Moving from the community level to the individual level, the third study investigated antecedents to dog owner care-related behaviour, specifically the concept of ‘duty of care’ as a motivational construct. It used a mixed methods approach to better understand the potential dimensions of duty of care, their interrelationships, and develop psychometrically valid tools to measure them in companion dog owners. One key finding was that many dog welfare problems may not be the result of lacking duty beliefs, but rather weaknesses in other ‘activation’ factors such as problem awareness. This then informed the final study. The final study further explored the concept of problem awareness and owner perceptions of dog welfare as potential targets for behaviour change interventions. This involved a 2 week field-study to examine relationships between owner perceptions of their dog’s welfare and animal-based indicators of dog welfare. This study also served as a pilot to trial the use of PetPace ‘smart collars’ as a practical approach to collecting dog welfare data in the home environment. Overall, there were few relationships between owner perceptions of welfare and animal-based indicators. These results provide preliminary evidence to support the development of a dog owner behaviour change intervention which targets owner perceptions of dog welfare and problem awareness. In all, this multi-disciplinary research has produced a significant contribution to the emerging field of human behaviour change for animal welfare. Throughout, this research has highlighted the complexities of owner behaviour, demonstrating the need for further research and development to ultimately improve the lives of companion dogs.
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ItemAssessment of thermotolerance in sheep based on changes in phenotypic and genotypic markers( 2022)Heat stress (HS) is one of the most significant single stressors affecting the global animal production by influencing physiology, development, growth, and reproduction, and the impact is likely to increase as global temperature rise. Given that the total magnitude of the stress experienced by an animal also depends upon the inherent individual genetic potential of the animal, identification of genetic traits for greater adaptability to extreme environmental conditions (high temperature, feed scarcity, water scarcity) is important to develop an effective strategy for climate change adaptation. Similarly, assessing the relative adaptive capacity of different sheep breeds to adverse climates could help the sheep industry to be resilient and adapt to climate change. In Australia, majority sheep population is comprised of Merino or Merino crosses, while some other breeds such as Dorper are gaining popularity due to their hardiness, low labor requirements, and high production efficiency. Dorper sheep are single-purpose hair sheep, tolerant of harsh environments. While 2nd cross Merino lambs are known for faster growth rates and superior carcass and meat quality traits, their ability for adaptation to higher temperatures is relatively unknown. Furthermore, there is lack of some simple and no invasive heat tolerant phenotypes, and molecular markers that could be utilized for the selection of heat tolerant sheep. This thesis investigated the potential phenotypes and biomarkers to assess thermotolerance, comparative thermotolerance of different sheep breeds, and optimized a non-invasive measure of HS in sheep using infrared thermography and machine learning. The first study compared the thermotolerance of Dorper and second cross (SC; Poll Dorset x Merino/Border Leicester) lambs based on changes in their phenotypes and molecular responses. Thermotolerance in these two genotypes were evaluated by exposing lambs to either thermoneutral (TN) or cyclic HS for two weeks and measuring physiological, metabolic factors, prolactin concentrations as well as difference in expressions of important genes related to production and adaptation, which are markers of HS response. Overall, two weeks of HS significantly altered their physiology, blood biochemical profile, prolactin concentration and gene expression patterns in both the sheep breeds. However, significant differences between genotype were evident in a series of parameters including water intake, feed intake, respiration rate (RR), rectal temperature (RT), skin temperature (ST), blood urea nitrogen (BUN), creatinine, non-esterified fatty acid concentrations (NEFA), prolactin concentrations, as well as heat shock protein A1A (HSPA1A), interleukin 2 (IL2) and prolactin receptor (PRLR) mRNA expressions. Comparatively lower influence of HS on several parameters indicated superior thermotolerance of Dorper, however further research involving a large population under natural grazing conditions is required. Dorper is a broad term that is frequently used to refer to both black-headed (Dorper) and white-headed (White Dorper) variants and any differences in their heat tolerance are unknown. A preliminary study was conducted to compare the thermotolerance of these two genotypes. This study was conducted on a commercial farm and twenty lambs of each (10 ewes and 10 rams; 3-4 months old) Dorper and White Dorper variants were selected. Based on the proposed weather forecast two collection days were selected: TN day and HS Day. Physiological responses [RR, RT and heart rate (HR)] and prolactin concentrations were measured on both the days. Genotype variations were observed only for RT and prolactin concentrations. Lower RT and prolactin concentrations were observed in White Dorper on both the days suggesting better thermotolerance of White Dorper to HS challenges. Given that the duration of heatwaves (acute vs chronic) influences effects on individual animals, the third animal experiment investigated the effects of different duration of HS on productive and adaptive traits of Merinos. Twenty-four (4-5 months old) healthy Merino sheep were selected and were randomly allocated to TN or cyclic HS treatments in a climatic chamber for four weeks. Overall findings indicated that Merino sheep can adapt to HS exposure for up to three weeks by enacting behavioral and physiological changes, without adversely affecting production metrics like growth. However, if heat exposure is prolonged beyond three weeks, sheep find it extremely difficult to maintain homeothermy, as evidenced by an increasing trend of physiological responses and a negative impact on growth rate. It is suggested that Merino sheep appear to be well adapted to short duration HS periods; however, HS mitigation measures would be needed where sheep are more likely to be exposed to long-duration heat waves. Identification of heat stressed animals under farm conditions is challenging due to the complexity of HS response and large population. From the perspective of the implementation of early interventions to mitigate HS, identification of heat stressed animals is crucial, subsequently measures that can be collected easily under farm conditions at a low cost are needed. A combination of computer vision algorithms and infrared thermal imaging (IRT) techniques were tested as a promising strategy to assess HS in sheep based on body temperature recorded from third animal study. This study aimed to test whether a combination of IRT and machine learning techniques can be applied to predict sheep RT when subjected to HS. In general, forehead and eye IRT temperatures had the strongest correlation with temperature-humidity index (THI) and RT. Furthermore, Bayesian Regularization with one hidden layer containing ten neurons with tangent sigmoid transfer functions demonstrated the highest correlation and performance. The model developed could be a quick and low-cost method for monitoring real-time body temperatures in sheep and detecting HS with minimal restraint. In absence of strategies for mitigating the effects of HS, sheep are likely to suffer HS over the hot summer months which are likely to be hotter and stay longer due to climate change and global warming. Therefore, there is continued need to improve knowledge around negative impact of HS and revisit husbandry practices to mitigate these effects. Therefore, the final sheep study, investigated the effects of provision of shade on behavior, physiological responses, and growth performance of Merino lambs exposed to natural southern Australian summer conditions. Sixty Merinos were randomly allocated to either pasture with shade (n=30; paddock with trees) or a pasture without shade (n=30; paddock without any trees). Sheep were grazing in the pastures as per the standard protocols followed on the farm with ad libitum access to water. The exposure to natural summer negatively influenced the behavior, physiology, and productive potential in grazing sheep. Further, access to adequate shade could be adopted as an effective ameliorative strategy to mitigate HS effects during natural summer, as evidenced by higher lying frequency, and lower RR, RT, seeking water troughs frequency, faecal and wool cortisol concentrations and prolactin concentrations, and improved average daily gain in sheep with access to shade. Overall, it can be inferred from a series of experiments that HS compromise thermoregulation in sheep leading to negative impact on their behaviour and production, though the degree of this influence may vary among different breeds. Comparatively, Dorper breed show superior adaptability to HS challenges compared to SC Merinos. Further, the results also indicate that chronic HS (>3 weeks) compromise both adaptive and production potential of Merino sheep and suitable strategies are required to ameliorate these effects. Combination of infrared thermography and machine learning techniques could be used to predict RT in sheep non-invasively. Finally, this research further confirms that providing access to shade is an effective ameliorative strategy to mitigate HS and improve growth rate in sheep during summer.
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ItemMetal-Phenolic Networks: From Fundamental to Agricultural Applications( 2022)Urea, as a nitrogen-rich fertilizer, plays a vital role in increasing and maintaining soil fertility, and crop yield. The efficiency of urea as a fertilizer reduces through ammonia volatilization, nitrification, denitrification, nitrate leaching to groundwater, and runoff. Nitrogen loss can be reduced through controlled-release ureas (CRUs), which can control the physicochemical release of urea in soil. Materials used for the fabrication of CRUs are mostly non-biodegradable polymers, which further spread pollutants into the environment. In an effort to reduce environmental impact, this thesis investigated the possibility of using metal-phenolic networks (MPNs) as a means of coating urea such that the MPN coating provides a physical barrier against water, controlling urea dissolution and release into soils. Self-assembly of MPNs in a non-aqueous solvent (acetonitrile) on urea granules was first conducted to engineer thickness-tunable coatings. Tannic acid and iron ions were chosen as model compounds for the assembly of MPNs. Varying operational conditions were assessed to determine the underlying mechanism for which MPNs were formed. Specifically, parameters, including the MPN self-assembly method, solution aging time, metal-to-ligand molar ratio, precursor concentration, and processing temperature all influenced the formation kinetics, thickness, and surface roughness of the films. Upon placement of coated urea granules in water the complete dissolution of urea occurred within 3-5 hours. The release rate of urea in water was controlled via the pH-dependent behavior of the self-assembled MPNs. Although urea coated with MPNs could control the dissolution of urea, the fabrication of CRU involved the use of solvent, which makes it not ideal for large-scale manufacturing processes where the volume of liquid media required makes handling difficult. Thus, in the second effort, a one-step mechanochemical grinding approach was utilized to synthesize MPNs in the absence of solvent. After an investigation of the mechanism of MPN formation in solvent-free conditions, the fabricated material demonstrates tunable mechanical resistance and stiffness that adjust with aging and thermal post-treatments. It is demonstrated that the encapsulated urea within MPNs can prolong the release period of nitrogen in the soil by up to 9 days depending on the type of post-treatment applied. This work provides a systematic understanding of the possible formation of MPNs using the self-assembly coating technique in non-aqueous media on urea granules (chapter 3) and encapsulation of urea in the MPN matrix (chapter 4). These simple fabrication methods open new chapters for utilizing environmentally friendly materials to control-the release of urea. The implementation of environmentally friendly materials is a key consideration in addressing the challenge of more sustainable and socially responsible agricultural production.
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ItemImpact of gestational heat stress on the fetus and neonatal piglet( 2022)High ambient temperatures adversely affect the welfare and reproductive performances of sows over the summer months. Gestating sows are particularly sensitive to heat loads with implications on both dams and their progeny. There is evidence that pig progeny born to sows that experience heat stress during gestation had altered phenotypes, such as increased carcass fatness and compromised lean tissue deposition. However, the cause for the phenotypic change remains largely unknown. Evidence from human epidemiological and animal experiments suggests that the postnatal growth of the progeny might be programmed by prenatal life. To better understand the aetiology, this PhD thesis aimed to investigate the effect of sow heat stress during critical stages of gestation (early to mid-gestation and late-gestation, respectively) on sow physiology and the development of fetuses, with a specific focus on the placental nutrition and oxygen transport function, fetal skeletal muscle development and perinatal survival of newborn piglets. The aims were achieved through climate-controlled studies using primiparous gestating sows (gilts). It is hypothesised that gestational heat stress caused placental insufficiency that would have a subsequent impact on fetal development and piglet survival. The thesis first aimed to investigate the changes in placental and fetal morphology in response to sow heat stress during early to mid-gestation. This time window was investigated because it is coincident with rapid placental functional development and fetal primary muscle fibre myogenesis. These experiments showed that gestational heat stress during this critical stage caused compensatory growth of the pig placenta and reduced fetal muscle fibre number density without affecting the body mass of the developing fetus at mid-gestation. Further transcriptome analyses of the placenta demonstrated that gestational heat stress altered the expression of genes and proteins that impaired placental major nutrient transport, including the glucose, amino acids and cation ions. These studies provided the molecular evidence underpinning the placental adaptation to gestational heat stress. In fetal skeletal muscle, gestational heat stress inhibited the muscle capacity for muscle-specific gene transcription and angiogenesis, and upregulated the pro-inflammatory responses, adipogenesis and fibrogenesis in a sexually dimorphic manner such that the differentially expressed genes were only detected in female fetuses. Collectively, the change in molecular pathways suggests a cross-link between sow gestational heat stress, placental insufficiency and compromised skeletal muscle development, possibly explaining the altered carcass phenotype of the progeny born to heat-stressed dams. Finally, the effect of heat stress during late-gestation was investigated on sow farrowing physiology, umbilical oxygen concentration and survival of newborn piglets. These studies demonstrated that, for the first time, gestational heat stress reduced umbilical oxygen supply from the placenta to the piglet at parturition, contributing to increased risks of piglet hypoxic stress, stillbirth, and liveborn mortality during the neonatal stage. Taken together, findings from the current thesis indicate that gestating sows are sensitive to high ambient temperatures with a particular vulnerability over the late-gestational phase. Placental insufficiency seems to be the primary consequence of sow gestational heat stress, which causes a carry-over effect on fetal development and perinatal piglet survival. Sow heat stress during early to mid-gestation adversely affected placental major nutrient transporter abundance and fetal skeletal muscle myogenesis. On the other hand, sow heat stress during late gestation and farrowing had a detrimental impact on piglet perinatal survival, possibly associated with umbilical oxygen insufficiency. Collectively, findings from the current thesis address the knowledge gaps on impacts of gestational heat stress on the sow, fetus and neonatal piglet, by adding that placental insufficiency, impaired fetal development and increased perinatal piglet mortality could be all associated with sow heat exposure during gestation. Furthermore, these findings suggest that intervention strategies are warranted to mitigate against the heat stress impact on pig production efficiency.
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ItemThe contribution of grape- and wine-derived volatile compounds to the perception of flavour in wine( 2022)Wine quality is determined by the local terroir, nature of grapevines, viticultural practices and vinification processes. Scientists have identified chemical compounds, typically volatiles, that can give desirable sensational attributes during wine tasting and potentially become chemical markers of high-quality wine. However, there is a lack of convincing statistical models using grape volatile composition to predict the resulting wine quality. Besides, there are still volatiles and other factors such as variations in biological factors of consumers to be revealed. Overall, this PhD thesis examines the influences of grape and wine volatiles on wine quality classification and perception during wine tasting.
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ItemTHE DEVELOPMENT OF NITROGEN ISOTOPIC DISCRIMINATION TO ESTIMATE URINARY NITROGEN EXCRETION AND MANURE AMMONIA EMISSION FROM SHEEP( 2022)A series of PhD studies was developed to investigate use of the nitrogen (N) isotopic fractionation or discrimination (known as delta15N) technique in sheep with two main objectives. Firstly, to investigate the relationship between N partitioning, particularly focused on the relationship of urinary N excretion (UN) and UN/N intake (NI; UN/NI), with plasma-feed N isotopic discrimination (plasma Delta15N; plasma delta15N – feed delta15N) in non-lactating sheep. Secondly, to explore the relationship between manure delta15N and NH3 emission from sheep manure. Treatment effects were assessed using ANOVA; the relationships between tested variables were analysed by regression analysis. The first N balance (NB) study (Chapter 3) was conducted to assess the effect of genetic merit (G) and feed allowance (F) and their interactive effects on N partitioning and plasma Delta15N in non-lactating sheep, whilst the second NB study (Chapter 4) explored the relationship of plasma Delta15N with UN and UN/NI of non-lactating sheep, offered three levels of dietary non-protein N. For Chapter 5, two 10-day in vitro studies were conducted to investigate: 1) the relationship between manure delta15N and NH3 emissions when incubating different manures (mixing manure with lignite and including grape marc (GM) in sheep diets to alter manure NH3 losses); and 2) the relationship between manure delta15N and manure NH3 emission of sheep, with manures comprising three different ratios of urine and faeces. Feed allowance had a more pronounced effect on N partitioning and isotopic discrimination than the Genetic effect (Chapter 3). Lower N use efficiency (NUE) and higher UN/NI were observed with lower F (P < 0.01). Evaluating treatment means alongside sheep literature data showed positive and negative linear relationships between UN/NI and plasma Delta15N, and NUE and plasma Delta15N, respectively (P < 0.01). In Chapter 4, positive and negative linear relationships between UN/NI and NUE with plasma Delta15N, respectively (P < 0.01), were observed. The two in vitro studies (Chapter 5) confirmed that manure-N content and urine to faeces ratio in the manure were the main factors to determine manure NH3 emission. Application of lignite directly to manure reduced NH3 emission significantly (P < 0.001). The observations from this PhD project indicated that plasma Delta15N can estimate UN/NI from sheep and the relationship between plasma Delta15N and UN/NI was linearly significant (Chapter 3 and 4). Additionally, a significant non-linear relationship was observed between manure delta15N and cumulative manure NH3 emissions (Chapter 5). These studies showed that delta15N may be developed as biomarkers for estimation of UN/NI and cumulative manure NH3 of non-lactating sheep