School of Agriculture, Food and Ecosystem Sciences - 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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ItemStudies on the prevalence, persistence and antibiotic resistance of enterococci from Australian dairy sources( 2016)This work was undertaken to determine the incidence of enterococci in raw milk and dairy products in the dairying regions of south-eastern Australia over a one-year period and to assess the ability of enterococci to persist in the dairy environment, survive pasteurisation and grow in dairy products. In addition, the risks associated with the presence of enterococci in dairy products was also considered. Enterococci were widespread in milk prior to manufacture, with lower counts occurring in raw milk in winter, which has not been reported in other studies internationally. The level of detection of enterococci in pasteurised milk was low and did not coincide with higher raw milk counts, indicating that the main enterococci population was heat sensitive. Although Enterococcus faecalis was the predominant species found in the raw milk, E. faecalis, E. malodoratus and E. faecium were detected in the greatest number of butter, Cheddar cheese and milk powder samples, respectively, suggesting that these species have inherent properties that enable them to survive processing conditions used in the manufacture of these dairy products. Thermal death determinations of the four main species identified from laboratory pasteurised milk (63 °C, 30 min) revealed that the E. faecalis isolates were the most heat sensitive, with the lowest z values (5.0-7.5 °C), while E. faecium, E. hirae and E. durans had the highest z values (8.5-9.8 °C). Thermoduric enterococci were able to grow at 4 and 7 °C in UHT milk. They were able to survive but not grow in butter, Cheddar cheese, cottage cheese, milk powder and yoghurt and in acidic and higher salt concentrations at 4 °C, indicating that dairy product environments limit the growth of enterococci. Genetic fingerprinting of enterococci at one of the dairy factories identified a persistent population of E. faecalis, which had streptomycin resistance and increased biofilm production, and inferred a link between these traits and persistence. The most frequently encountered antibiotic resistances were to streptomycin and tetracycline, which, along with chloramphenicol and erythromycin resistance, could be transferred to both E. faecalis and E. faecium but in limited situations to E. hirae and Listeria monocytogenes. Transfer to E. hirae has not been previously demonstrated, which is significant in context of this species increased resistance to heat treatment. The isolates were also mated in a multi-strain biofilm on stainless steel coupons in milk incubated at 10 and 25 °C. No transconjugants were detected under these experimental conditions. Results of this study found that enterococci in the south-eastern Australian raw milk supply possessed multiple virulence factors and antibiotic resistances, which were at times transferrable between species and genera. While the majority of enterococci were eliminated with pasteurisation, some enterococci were heat-resistant, meaning that enterococci with virulence factors and antibiotic resistance could gain entry into the food supply if these traits were present in such isolates. However, resistance to the antibiotic of most concern, vancomycin, was not found in E. faecalis, a major species associated with medical issues. Although there is a theoretical risk of enterococci containing medically-undesirable traits entering the food supply, their ability to grow in products may be limited by the nature and storage conditions of the products.
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ItemAssessing the value of novel perennial ryegrasses (Lolium perenne L.) for the Australian dairy industry( 2014)The value of increasing the metabolizable energy (ME) concentration of grass using a genetically modified high-fructan perennial ryegrass (Lolium perenne L.)(‘GM ryegrass’), was assessed in this thesis. This included: an assessment of the expression of the fructan trait and effects on rumen fluid chemistry (in vitro), simulating potential profitability and greenhouse gas (GHG) emission effects on-farm, and the scale and distribution of benefits from changing the ME concentration of perennial ryegrass to the Australian dairy supply chain. The GM ryegrass was associated with an increase in herbage dry matter (DM) energy concentration between 0.8 megajoules (MJ) and 1.74 MJ of ME per kilogram (kg) of DM. In vitro experiment results indicate increasing the concentration of fructan in the GM ryegrass did not adversely affect rumen pH or methane production. Two representative dairy farms (in Terang in south-west Victoria and in Elliott in Tasmania) were used to provide context for the assessment of the value of increasing the ME concentration of perennial ryegrass herbage. Deterministic economic values, in Australian dollars (AUD) of AUD237/hectare(ha).year and AUD592/ha.year for a 1MJ/kg DM increase in pasture energy concentration were calculated using the replacement cost method for Terang and Elliott dairy farms respectively. Further economic modelling using a mechanistic pasture growth model was used to assess how farm operating profits (OP) changed when additional energy from the GM ryegrass was utilized through various management practices. Results indicate even greater changes in OP could be achieved compared to the replacement cost method if energy was utilized with greater milk production per cow. When energy was utilized through greater milk production per cow a 1MJ/kg DM increase in energy concentration was associated with an AUD482/ha.year mean increase in OP in Terang and a AUD783/ha.year increase for Elliott. Dilution of GHG emissions across the additional milk produced from cows consuming the GM ryegrass was estimated to reduce GHG emissions intensity (EI) of milk by 10% in Terang and 13% in Elliott compared to the Base Scenario. Mean total benefits to the Australian dairy supply chain from adoption of the GM ryegrass based on a 1MJ increase in energy concentration were estimated between AUD205 million and AUD300 million (as a net present value) over a 15 year period. This study also provides sensitivity analysis of the results to changes in key assumptions such as the rates of adoption and elasticities. Estimations of benefit at the Australian dairy supply chain level were calculated using an equilibrium displacement model assuming a 10% discount rate and farmers who adopted the GM ryegrass (‘adopter’ farmers) renovated 10% of their farm area into the GM ryegrass. Australian consumers were estimated to receive most (70%) benefit from farmer adoption of the GM ryegrass, followed by farmers and suppliers of the seed technology (26%). Benefits suppliers of the seed technology receive will depend on how the GM ryegrass is licensed, competition amongst seed companies, and how rapidly farmers adopt the GM ryegrass. Results from this thesis therefore supports the hypothesis that increasing expression of fructan concentration in perennial ryegrass could increase the energy concentration of herbage DM to provide significant increases in OP and reductions in GHG EI for farmers who adopt the technology. Results also provide valuable information for decision-makers for allocating appropriate resources toward deregulation of this GM ryegrass.
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ItemGoverning agriculture for rural community sustainability: a case study in the Australian dairy industry( 2015)This thesis focuses on the concept of industry governance to examine the processes shaping agricultural change in Australia. It aims to identify how agricultural industry governance can better support rural community sustainability, understood as having social, economic, environmental and equity dimensions. I adopt a conceptual framing of industry governance as a process of collective action involving actors and activity in three spheres: place, industry and state. I use actor-network theory (ANT) to trace how industry governance activity arises from associations between human and non-human actors. This theoretical choice seeks to make research a practice that reveals opportunities for things to be different, rather than one that adds weight to existing explanations of why things are as they are. The research design consists of a single case study in the dairy industry in north-east Victoria, Australia. I analyse the organisational arrangements and processes entailed in industry governance, including processes occurring within one local community – the Mitta Valley. I also examine the social and material practices revealed in a regional-scale industry development project – the Alpine Valleys Dairy Pathways (AVDP) project. Data generated include seventy interviews with dairy farmers, other community members and governance actors, three years of participant observations of the AVDP project and content analysis of relevant documents including news media. Cognisant of the opportunities and risks of my close engagement with research participants' reflection and action, I enacted my research practice as systemic inquiry. People in the Mitta Valley see agriculture, and particularly dairy farming, as highly desirable activities that build on the strengths of their place, and that could help their community sustain itself into the future. However, they have doubts about the feasibility and desirability of continuing the existing agricultural development trajectory toward larger, more intensive farms. I found that the dairy industry, through the industry ‘sustainability’ agenda, is engaging with citizens' and customers' demands for improved environmental management and animal welfare. However, industry governance continues to shape change toward larger, more intensive and more highly-capitalised farms. There is a current focus on promoting more diverse farm business models (or organisation forms), potentially involving separation of land ownership, farm business ownership, and farm management responsibility. Industry and government actors are not examining the potential implications of such changes for rural communities. Understanding governance as collective action, using the conceptual tools of ANT, provides insight as to why this is the case. I identify 'industry growth' as a boundary object that is integral to the establishment of collective action, and that enacts a positive and unproblematic relationship between dairy industry development and community benefit. Governing agriculture for community sustainability requires governance actors representing the interests of communities to be included in industry development planning and action, and to be prepared to question the assumed benefits of 'growth', in the light of the range of processes that communities identify as contributing to their sustainability. This change in governing practices could result in changed emphases within industries' practice change interventions, to shape growth in accordance with communities' collective interests.
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ItemSuitability of subsurface drip irrigation for sustainable pasture production in the Riverine Plain( 2012)The dairy industry of the Riverine Plain in the southern Murray-Darling Basin has traditionally relied on border-check (B-C) irrigation for year round productivity of perennial pasture. Recent prolonged drought conditions coupled with unprecedented low water allocations severely constrained B-C pasture irrigation. Also, concern about the ecological impacts of water extraction and its use for irrigation in the Murray-Darling Basin is increasing. Consequently, farmers and resource managers are considering the role of subsurface drip (SSD) irrigation in improving pasture irrigation sustainability. SSD irrigation is a water efficient technology that delivers water and nutrients through emitters directly to points within a plant’s rootzone, often leading to improved crop yield. Past SSD research has focussed on row crops including vegetables, fruit, maize and lucerne. SSD irrigation of pasture on Riverine Plain soils represents a significant departure from this past research in three main respects: (1) the pasture will be grazed by dairy cattle, (2) pasture production occurs across the full soil surface rather than as individual plants separated by bare soil, and (3) Riverine Plain soils are duplex, with irrigation performance influenced by contrasting horizon hydraulic conductivity, soil shrinkage tendencies and the role of macropore flow in infiltration. Given SSD irrigation’s substantial cost, a greater understanding of likely water, pasture productivity and environmental benefits is necessary before its use is recommended for pasture production in the Riverine Plain. The overall objective of this study was to identify the combinations of SSD irrigation design (tape spacing) and operation (irrigation frequency) that deliver optimal environmental performance for perennial pasture irrigation across the range of soils found in the Riverine Plain. A three step approach was used. Firstly, replicated field experiments were conducted at two case study sites, allowing rigorous quantification of pasture accumulation, water and nutrient movement on duplex soils with differing B horizon permeability. Combinations of tape spacing (0.6, 1.0 and 1.4 m) and irrigation frequency (daily or 4 days irrigation) were imposed. The second step assessed the ability of the Hydrus-2D model to predict the hydrological processes observed at the case study sites, with the intention of then applying the validated model in the third step, investigating SSD design and operation impacts on water and nutrient movement for the major soil classes of the Riverine Plain. The field experiments showed that seasonal pasture accumulation exhibited sensitivity to tape spacing and irrigation frequency whereas pasture botanical composition was insensitive.The degree of sensitivity in pasture accumulation differed markedly between the two sites, reflecting soil characteristics. Where the soil B horizon was moderately permeable (East Shepparton fine sandy loam, with B horizon saturated hydraulic conductivity of ~10 mm/h), pasture accumulation was reduced by 17% as tape spacing increased from 0.6 m to 1.4 m. Where the soil B horizon had low permeability (Lemnos loam, with B horizon saturated hydraulic conductivity of ~5 mm/h), pasture accumulation was insensitive to tape spacing or irrigation frequency. Pasture yields on the soil with the moderately permeable B horizon were 30% lower than on the soil with the low permeability B horizon. The extent to which tape spacing and irrigation frequency affected water and nutrient movement was controlled by the subsoil’s hydraulic behaviour. At the seasonal scale, tape spacing and irrigation frequency had no consistent impact on water balance components at both sites. Universally, minimal runoff occurred and deep percolation was the main pathway for water loss. Subsoil hydraulic behaviour controlled rootzone soil moisture redistribution and the fate of applied irrigation water, the mechanisms of deep percolation and its consequence. Soil moisture and deep percolation were more sensitive to irrigation frequency than tape spacing. On the soil with the moderately permeable B horizon, soil moisture 0.1 m above the tape responded to 4 days irrigation but not to daily irrigation. Nitrate-N travelled with irrigation water, consequently tape spacing had little impact on nutrient movement while irrigation frequency was important for the soil with the moderately permeable B horizon. Use of Hydrus-2D as a tool to generalise the assessment of SSD performance was attempted. However, in validating Hydrus-2D’s performance in simulating the case studies it was clear that Hydrus-2D did not capture key hydrological processes. Hydrus-2D was unable to predict water and solute movement with sufficient accuracy due to its inability to account for macropore flow, which is a recognised characteristic of Riverine Plain soils. Subsequent identification of optimal SSD design and operation combinations for environmental performance thus drew solely on the experiment findings. For texture-contrast duplex Riverine Plain soils, SSD operating regime (irrigation frequency) has greater impact on water and nutrient movement than SSD design (tape spacing), but the degree of impact depends on the subsoil’s hydraulic properties. For duplex soils with moderately to highly permeable subsoils (for example East Shepparton fine sandy loam), irrigation duration will dictate the balance between gravity-dominant downward movement or lateral and upward redistribution of irrigation water. On duplex soils with low permeability subsoils (for example Lemnos loam), the subsoil restricts downward movement, allowing water to spread laterally and upwards regardless of SSD operating regime. Where the subsoil exhibits very low permeability (for example Congupna clay, with B horizon saturated hydraulic conductivity of ~1 mm/h), surface runoff may become more important as a loss pathway. Provision of incentives would improve economic feasibility of SSD in pasture production, if the environmental benefits to the wider community warranted such intervention. This study has highlighted potential environmental advantages and disadvantages of SSD irrigation, clarifying where its use is appropriate. Field studies demonstrated that SSD was not ideal on soils with moderately to highly permeable subsoils, leaving sprinkler irrigation as the most appropriate option for irrigators. For other Riverine Plain soils, SSD irrigation has clear advantages over B-C irrigation in the minimisation of evaporative water loss and surface runoff. The absence of surface water and the reduction in surface runoff in turn will assist nutrient management. Use of fertigation with SSD will reduce volatilisation loss of fertiliser, but this may be offset by loss of nitrate-N in drainage water. Similarly, managing deep percolation from SSD may prove more challenging than managing runoff from B-C irrigation. SSD depends on a pressurised water supply, has high embodied energy and thus higher energy requirements and associated greenhouse gas generation than B-C irrigation. Ultimately, the question of whether adoption of SSD irrigation substantially improves overall pasture irrigation sustainability or not will have to be assessed on a case by case basis, given its dependence on current farm practices.
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ItemA systems approach evaluating alternative dairy feeding strategies in south-east Australia( 2012)The Australian dairy industry relies primarily on pasture for its feed supply. However, the variability in rainfall negatively effects plant growth, leading to uncertainty in dryland feed supply, especially during periods of high milk price. New (complementary) systems combining perennial ryegrass with another crop and/or pasture species have potential to mitigate this seasonal risk and improve productivity and profitability by providing off-season feed. To date, the majority of research studying the integration of alternative crops into pasture-based systems has focused on substitution and utilisation of alternative feed sources. There has been little emphasis on the impacts of integration of forage crops on the production of surpluses or deficits in feed supply (pasture and pasture products such as hay and silage) for subsequent lactations. This study, unlike others where pasture consumption is estimated, uses actual annual pasture consumption rates measured over four years from an on-farm trial. In addition, while the ultimate aim of adopting different feeding systems is to increase productivity and profitability of dairy farmers in Victoria, the benefits and costs associated with transitions of systems have to be addressed. These include whether alternative feeding systems produce different amounts of greenhouse gas (GHG) emissions, and whether the proportions of carbon-based and nitrogen-based emissions produced in each system are comparable. Further, if a direct cost is placed on carbon emissions, whether Australian dairy farmers will seek mitigation strategies to reduce their GHG emissions. The impact of a direct price of carbon emissions on dairy farm operating profits has not been widely studied in Australia. This thesis examines and analyses actual systems data from two pasture-based feeding systems trials conducted in southern Australia. The systems examined are a ryegrass-based (RM) system comprising pasture and pasture silage and a complementary forage-based (CF) system comprising double-cropping (winter cereal crop followed by a summer grazing crop) as well as pasture and pasture silage. A comparison of pasture production and pasture consumption profiles of the two pasture systems revealed that both are under supplied during the months of July, December, January, February and March (with at least a 50% probability). Feeding strategies were developed for the rest of the production year when the pasture production exceeded the pasture consumption. The integration of double-cropping systems into pasture-based dairy production systems in south-east Australia was investigated for providing feed at critical times of the production period to further increase milk production. The partial life cycle assessment (LCA) used to evaluate the GHG emissions produced in each feeding system indicated that the RM and the CF systems produced 9.6 t and 12.3 t of carbon dioxide equivalent (CO2-eq) emissions per ha respectively. This equalled to 7.4 kg and 7.1 kg CO2-eq emissions per kg milk solids (MS) produced respectively. A nitrogen (N) surplus balance technique showed that the ratio of N in milk to N in all the inputs used was similar, 25.2% and 26.6%, for the RM and the CF systems respectively. A novel risk analysis comparing the variability in income in response to different prices on carbon emissions was also conducted in this study. Imposing a carbon price ($20–$60) and not changing the systems reduced the operating farm operating profits by 28.4% in the RM systems and 25.6% in the CF system compared to a scenario where no carbon price was imposed. In conclusion, production and utilisation of home-grown feeds will remain paramount among the south-east Australian dairy farmers to maintain and increase profitability in this competitive dairy sector. However, the risk associated with the higher operating profits in the CF system requires further evaluation. There is opportunity for future studies to focus on the impacts of different mitigation and adaptation strategies and policy impact on farm operating profit. Further evaluation and improvement of the assumptions and model predictions as well as the monitoring technologies are suggested to enable further policy research.