Veterinary Science - Theses
Permanent URI for this collection
Search Results
1 - 10 of 19
-
Item
-
Item
-
Item
-
ItemA study investigating the incidence and associated risk factors of heifer mastitis in the Macalister Irrigation District( 2013)The project aimed to assess the incidence, causative pathogens and risk factors for mastitis in primiparous heifers in the Macalister Irrigation District (MID). Additional aims included analysis of the effect of mastitis on production, lactation length and risk of removal from the herd. Data was collected from 19 farms over a period of two years. This included a retrospective analysis of data collected in 2009, and prospective data collection in 2010. Information such as management practices, treatment records, individual cow cell counts, production data, cull records and bulk milk cell counts were collected in both years. Additional data gathered in 2010 included microbiological culture results from both clinical and subclinical cases of mastitis, and recording of health events. Overall 11.3% of the heifer cohort in this study suffered from at least one case of clinical mastitis (CM) during the first lactation. Heifers were particularly at risk of mastitis early in lactation, with 65.7% of cases occurring within 30 days in milk, compared to 37.7% in mature cows in the same period. Strep. uberis was the bacteria most commonly isolated from quarter cases of clinical mastitis (48.1%) and from heifers diagnosed with subclinical mastitis (15.6%). The use of an internal teat sealant pre-partum had the greatest effect on the odds of CM within 30 days of calving (CM0-30d) (OR 0.44 CI 0.28-0.68 P<0.001) followed by calving in 2010 (OR 1.71 95% CI 1.31-2.33 P<0.001). Herd size as a continuous variable was found to have a quadratic effect on CM0-30d. Adverse health events such as dystocia and lameness were assessed as risk factors for mastitis within a smaller subset of herds, and no relationships were found between CM0-30d and any of these events. Similarly no significant associations were detected between CM0-30d and production outcomes, lactation length or the odds of removal from the herd. This research increases our understanding of heifer mastitis within an Australian context, and validates certain risk mitigation strategies specific to heifers in Australian pasture based systems.
-
ItemComparative analyses of key parasitic helminths through transcriptomic data integration using bioinformatics( 2013)Parasitic helminths (worms) of humans and animals cause diseases of major socioeconomic impact worldwide. Considering their impact, the emergence of drug resistance and the absence of commercial vaccines, there is a growing demand for alternative intervention strategies to control such worms. Clearly, improved knowledge and understanding of the molecular biology and biochemistry of parasitic helminths should underpin the development of new methods for the treatment and control of parasitic helminth infections. Advanced molecular and informatic technologies are providing unique opportunities to explore the systems biology of helminth at substantially reduced cost and time. Despite these advances, the amount of functional information that can be inferred from sequence data is still limited. The studies described in this thesis create a framework for the integration of sequence data from a range of parasitic helminths, allowing for improved annotation and comparative analyses and leading to new insights into the molecular and system biology of selected parasitic helminths. This framework enabled comparative studies of two key lungworms of ruminants, with a focus on parasite-host interactions, and provides a foundation for many future studies of parasites.
-
ItemStructural and functional investigations of a chemokine binding protein from equine herpesvirus-1( 2013)Equine herpesvirus-1 (EHV-1) and equine herpesvirus-4 (EHV-4) are members of the Alphaherpesvirinae subfamily in the Herpesviridae family. Both EHV-1 and EHV-4 are endemic equine viruses worldwide. Infection with EHV-1 has significant health effects for equine populations by causing respiratory disease, abortion, perinatal mortality and severe neurological disease. Equine herpesvirus-4 predominantly causes respiratory disease. Abortion, perinatal mortality and neurological disease are rarely associated with EHV-4 infection. Equine herpesvirus-1 and EHV-4 both encode glycoprotein G (gG). Homologues of this protein are also present in most other alphaherpesviruses. Glycoprotein G encoded by EHV-1 is a chemokine binding protein, although no chemokine-binding activity has been demonstrated for EHV-4 gG. This project studied the ability of EHV-1 gG to bind to various recombinant chemokines, cytokines and defensins. The binding activity of full length and truncated foms of recombinant EHV-1 gG were compared using enzyme linked immunosorbant assays (ELISAs). The study also investigated the ability of recombinant EHV-1 gG to function as an immunomodulator in a mouse model using influenza virus. The immunomodulatory properties of recombinant EHV-1 gG were compared to those of recombinant EHV-4 gG and recombinant infectious laryngotracheitis virus (ILTV) which is an alphaherpesvirus of chickens. Equine herpesvirus-1 gG bound to recombinant chemokines from various species (human, mouse, equine), as well as recombinant human and mouse cytokines, and recombinant equine alpha-defensin-1. The chemokine binding of the truncated form of EHV-1 gG was similar to that of the full length recombinant EHV-1 gG. In mice, no significant difference in immunoglobulin levels was observed in animals that received infectious or inactivated influenza, compared to those that received infectious or inactivated influenza along with recombinant EHV-1, EHV-4 or ILTV gG. Recombinant ILTV gG co-delivered with infectious influenza resulted in a significant decrease in CD8 cells compared to infectious influenza alone. The co-delivery of EHV-4 gG resulted in a significant decrease in CD8 cells in infectious influenza studies and a significant increase in CD8 cells in inactivated influenza studies. No inflammatory cytokine or chemokine responses were detected in these studies using cytometric bead arrays. The results showed an influence on the cell mediated immune response. This project improves our understanding of the role of gG and the effect of its ability to bind to chemokines, cytokines and defensins. This project contributes to our understanding of the disease pathogenesis of EHV-1 and other alphaherpesviruses that encode gG. This project also brings potential benefits through the characterisation of an immunomodulatory compound that may have therapeutic application.
-
ItemAnti-inflammatory effects of clenbuterol hydrochloride on leukocyte activation in the horse( 2013)The work reported in this thesis aimed to investigate the potential anti-inflammatory effects of clenbuterol hydrochloride in the treatment of equine endotoxaemia. Beta adrenergic agonists, such as clenbuterol hydrochloride reduce leukocyte activation and cytokine production through the up regulation of cyclic adenosine monophosphate. Investigations measured pro-inflammatory cytokine production (IL-1β and TNFα) by equine leukocytes, following stimulation with endotoxin, peptidoglycan and lipoteichoic acid and treatment with clenbuterol hydrochloride during in vitro and in vivo studies. The study also aimed to develop a model enabling correlation of pharmacokinetic and pharmacodynamic drug properties in order to predict an optimum dosing regimen for novel anti-inflammatory agents. The results of the study indicated that clenbuterol hydrochloride has significant anti-inflammatory effects on equine leukocytes challenged with Gram negative and Gram positive bacterial toxins in in vitro assays. Clenbuterol hydrochloride was most potent at inhibiting TNFα production in response to endotoxin, with the effects on peptidoglycan and lipoteichoic acid only being significantly inhibited at much higher clenbuterol hydrochloride concentrations (>10-6 M). Also a marked reduction in lipopolysaccharide stimulated IL-1β cytokine production following treatment with clenbuterol hydrochloride was recognised. In in vivo models of equine endotoxaemia, pre-treatment with oral clenbuterol hydrochloride caused a significant reduction in the peak rectal temperature and peak plasma TNFα concentrations. A model correlating clenbuterol hydrochloride pharmacodynamics and pharmacokinetics was developed. Clenbuterol may have a beneficial role alongside non-steroidal anti-inflammatory drugs and other previously investigated therapies in the treatment of inflammation associated with sepsis in horses. Further investigations in clinical cases of equine endotoxaemia are essential prior to the recommendation of clenbuterol hydrochloride as an adjuvant anti-inflammatory agent in the treatment of systemic inflammation.
-
ItemDetection of subchondral bone pathology in the fetlock joint of Thoroughbred racehorses( 2013)REASONS FOR PERFORMING STUDY: Two common subchondral bone injuries occur within the fetlock joint; palmar osteochondral disease and condylar fracture of the distal metacarpus. Both result in lameness, whereas condylar fracture can potentially be life threatening. Pre-existing pathology is commonly identified in horses with condylar fractures, detection of which prior to fracture would have both welfare and economic benefits for the racing industry. However the close spatial association of these two conditions complicates imaging of the distal metacarpus/metatarsus. AIMS: To describe patterns of radiopharmaceutical uptake in fetlock joints of Thoroughbred racehorses and to evaluate racing performance post-scintigraphy and to assess the potential of high-resolution peripheral quantitative computed tomography to predict condylar fracture in Thoroughbred racehorses by imaging the subchondral bone of the distal palmar metacarpus and the cortical bone of the mid diaphysis. HYPOTHESES: Increased radiopharmaceutical uptake (IRU) in the metacarpal (MC) and metatarsal (MT) condyles is more common than IRU in the parasagittal grooves and is associated with poorer post-diagnosis performance than controls. Horses with lateral condylar fracture would have greater bone volume fraction, greater localised subchondral bone thickness at the fracture site and that articular surface fissures would be more prominent in the contralateral limb than controls. METHODS: Scintigraphic evaluation of the fetlock region - A retrospective, case control study was performed using horses undergoing scintigraphy for the investigation of lameness or poor performance. Location of IRU within the fetlock region was identified and graded in Thoroughbred (TB) racehorses presenting for scintigraphic examination. Performance variables were determined from race records for horses with moderate/marked MC/MT condylar IRU (cases), all other horses undergoing scintigraphy (scintigraphy controls), and age/sex matched controls from the last race in which a case participated (controls). Statistical analysis included quantile regression, Fisher’s exact test, Kaplan-Meier survival curves, log-rank test and Cox regression. High resolution peripheral quantitative computed tomography as a predictor of condylar fracture - A prospective, cross-sectional, case control study was performed using limbs from all TB racehorses that died or were euthanased on Victorian metropolitan racetracks between June 2007 and June 2009 (n=37). Groups were assigned as follows: horses with MC fractures with a condylar component (cases, n=13); horses with no limb fracture (controls, n=8); horses with fracture in other bones or disruption of suspensory apparatus (other fatal musculoskeletal injuries, n=16). The palmar distal aspect was removed and a 5cm length of midshaft of MC created and stored in 70% ethanol. The palmar condyles of MC and midshaft examined with high resolution peripheral quantitative computed tomography (HR-pQCT) and morphometric parameters computed. Statistical analysis included logistic regression and Spearman’s correlations. RESULTS: Scintigraphic evaluation of the fetlock region - Metacarpal/MT condylar IRU was identified in 103/220 horses with only 3/220 having parasagittal IRU. Moderate/marked IRU was identified in the forelimb MC and hindlimb MT condylar regions in 62 and 48 horses respectively with palmaromedial and plantarolateral IRU most common. Forelimb cases had fewer starts (P<0.001), reduced earnings (P<0.001), fewer wins (P=0.03) and fewer overall places (P<0.001) than controls. Hindlimb cases had fewer starts (P=0.003) and reduced earnings (P=0.01) than controls. Cases were more likely to return to racing later than controls following a rest period (P=0.003). Cases were older than scintigraphy controls (P<0.001). High resolution peripheral quantitative computed tomography as a predictor of condylar fracture - No significant differences were identified in HR-pQCT variables of distal MC and midshafts between cases and controls. Epiphyseal BV/TV was greater in injured limbs of horses with any fatal limb injury compared to controls (OR 1.20, 95% CI 1.01-1.42, P=0.034). An epiphyseal BV/TV >0.74 resulted in a sensitivity of 82.8% and specificity of 62.5% in identifying horses with fatal limb injury. In horses without condylar fracture, increased subchondral bone thickness was associated with POD lesions in the adjacent condyle (rs=0.65, P<0.001). CONCLUSIONS: The identification of condylar fractures prior to catastrophic injury remains challenging. Condylar fractures are rarely identified using bone phase scintigraphy and this may be because lameness is not observed by owners and trainers prior to fracture. Even with high resolution imaging of the distal metacarpus, early condylar fracture detection is challenging although increased BV/TV of the distal metacarpus may be useful for determining horses at risk of any fatal breakdown injury. HR-pQCT of the third metacarpal bone midshaft appears to be of no value for predicting fatal injury. Racehorses with moderate/marked condylar IRU have a shortened racing career, are less successful than age/sex matched controls and are older than other racehorses presented for scintigraphy. POTENTIAL RELEVANCE: Effective screening for condylar fractures prior to catastrophic breakdown would require imaging of horses that are not showing clinical signs of lameness or poor performance. Applying advanced imaging to all horses at regular intervals is not only cost prohibitive but the current evidence suggests it is unlikely to be highly effective. POD appears to be performance limiting in Thoroughbred racehorses.
-
ItemThe effects of post-partum and pre-mating start date weight change and production level on reproductive performance in lactating cows in a seasonal calving, pasture-based system( 2013)Retrospective fertility data from a 600 cow, predominantly Holstein-Friesian, seasonal calving herd in south west Victoria was analysed to ascertain fertility trends on the farm over 10 years. Prospectively, daily body weights were collected and analysed with reproductive and production data to establish associations between weight change and production level both post-partum and pre-mating start date and reproductive performance. Body weights from automated walkover weighing scales at the exit to the dairy were collected, filtered and analysed to determine weight change trends post-partum (PP) and pre-mating start date (MSD). Herd reproductive parameters were established from calving dates, AI dates and early ultrasound pregnancy testing results. Production data from inline milk meters were collected and analysed to provide measures of PP and pre-MSD production level. The effects of PP and pre-MSD weight change and production variables on reproductive performance, together with the confounding variables age, time calved and calving induction, were statistically analysed to establish predictors of poor reproductive performance. ACCURACY OF THE SCALES Initially, a study was performed to determine the repeatability of the walkover scales and their agreement with static scales. Forty-six cows from the study herd were weighed once using a set of static scales and repeatedly using the automated walkover weighing system. The walkover weighing system showed substantial agreement with the static scales when assessed using Lin’s concordance correlation coefficient. This contrasted with limited agreement when assessed using Bland and Altman’s method, largely due to poor repeatability. Removal of a single outlier from the data set increased all measures of agreement and repeatability. Cow misbehaviour during walkover weighing accounted for many of the larger weight discrepancies. The limited agreement and poor repeatability suggest that the automated weighing system is inadequate for detecting small body weight differences in individual cows based on comparisons of single weights. Excluding outlier weights and comparing means of 7 consecutive daily weights may improve agreement sufficiently to allow meaningful assessment of small short-term changes in automated weights. WEIGHT CHANGE TRENDS Once an accurate weight dataset was established through data filtration, weight change trends over time were established. Linear regression lines were fitted through all filtered weights recorded between days 8 to 28 and 29 to 49 PP and days 42 to 22 and 21 to 1 pre-MSD. Positive slopes were assigned ‘Up’ trend and negative slopes were assigned ‘Down’ trend resulting in one of four possible double weight trends – Down Down (DD), Down Up (DU), Up Down (UD) and Up Up (UU) - for both PP and pre-MSD weight change. EFFECTS OF WEIGHT CHANGE AND PRODUCTION ON REPRODUCTIVE PERFORMANCE The most important factor affecting reproductive performance was duration of time calved. An increased time from calving to MSD resulted in improved measures of reproductive performance. PP weight change, age and yield at 100 days-in-milk were also significant predictors of submission by 3 weeks with PP DU cows having 1.7 times the odds of being submitted compared to DD cows. Three to 5 year olds had almost 3 times the odds of being submitted compared to 2 year old cows. Producing an extra 100L of milk by 100 days-in-milk resulted in 5% reduced odds of being submitted by 3 weeks. Pre-MSD weight change was a significant predictor of not being in-calf by 21 weeks. Pre-MSD DU, UD and UU cows had reduced odds of not being in-calf compared to DD cows. Cows producing an extra litre of milk daily in the 3 weeks prior to MSD had 5% reduced odds of submission by 3 weeks and 7% increased odds of becoming an NVO. In summary, reduced reproductive performance was observed in first calving heifers, animals not long calved, DD cows and high producing animals. The ability to identify these high risk animals prior to MSD could assist reproductive management, either through modified nutritional supplementation, prompt implementation of hormonal treatments or through alteration of insemination choices. Assessing the efficacy of these suggested management modifications at improving reproductive performance of high risk animals was beyond the scope of this study but provides suggestions for further research.
-
ItemHerpesviruses in Australian marsupials( 2013)Herpesviruses are ubiquitous, enveloped DNA viruses that have been identified worldwide in most vertebrate and in several invertebrate species. Within the Marsupialia, several different herpesvirus species have been detected across various macropodid species, and more recently in koalas and antechinus species. Infection may be subclinical, and the capacity to induce lifelong infection with periods of latency and intermittent reactivation is a feature common to all herpesviruses, although the mechanism by which this occurs varies according to the individual herpesvirus species. In macropodids, herpesviruses have been associated with outbreaks of disease and mortality, and clinical signs may include conjunctivitis, oral and/or cloacal ulceration, or sudden death associated with disseminated pathology including widespread visceral necrosis and inflammation. This study sought to evaluate the prevalence and significance of individual herpesvirus species in various free-living and captive populations of Australian marsupials. Swab samples from 397 marsupials principally including eastern grey kangaroos (Macropus giganteus), other members of the Macropodidae and the Potoroididae families, koalas (Phascolarctos cinereus), Tasmanian devil (Sarcophilus harrisii), common wombats (Vombatus ursinus) and bandicoot species were collected and a universal herpesvirus nested PCR protocol utilised to determine the prevalence of active herpesvirus infection in these animals. Serum neutralisation tests and PCR on tissue samples were also performed for some animals, and virological culture on wallaby fibroblast cells and newly developed wombat kidney cells was attempted for several of the novel herpesvirus species identified. Prevalence of active herpesvirus infection varied across the marsupial species, ranging from 0% in some of the wallaby species, to 25% in eastern grey kangaroos, 33.3% in koalas, 34% in Tasmanian devils and 45.5% in the common wombat. Seroprevalence of antibodies against macropodid herpesviruses-1 and -2 was also variable, from 0% prevalence in koalas and some of the wallaby species, 66.7% in common wombats and as high as 92% in the eastern grey kangaroo and 100% in the swamp wallaby. Sequencing of a conserved portion of the DNA polymerase gene identified seven novel herpesvirus species from six marsupial hosts, and phylogenetic analysis classified each of these novel herpesvirus species into their respective subfamily groups, namely the Alphaherpesvirinae (vombatid herpesvirus 3) and the Gammaherpesvirinae (macropodid herpesvirus 5, potoroid herpesvirus 1, dasyurid herpesvirus 2, vombatid herpesvirus 1, vombatid herpesvirus 2 and peramelid herpesvirus 1). Development of a wombat tissue cell culture facilitated the successful isolation of two of the novel wombat herpesviruses, vombatid herpesviruses-1 and -2, in addition to phascolarctid herpesvirus 1, a koala gammaherpesvirus that had not been previously isolated. Epidemiologic analysis was performed where permitted by sample size, and identified various factors in association with active herpesvirus infection. Results varied significantly between the different marsupial species evaluated, and likely reflect differences in the biology of the respective herpesvirus species, biological and ecological differences between marsupial hosts, and environmental factors. The significance of herpesvirus infections identified in marsupial hosts is discussed with respect to the clinical signs observed in infected animals, and the biological and ecological threats facing individual marsupial species including: ongoing habitat destruction as a result of urbanisation, logging and natural disasters; the effects of climate change; predation by introduced mammals; and concurrent diseases of ecological importance. Possible transmission routes for individual herpesvirus species are suggested and scope for further research discussed. This study has broadened the mammalian host range in which natural herpesvirus infections have been found and identified seven novel herpesvirus species. Whilst the significance of these herpesviruses remains unclear, the presence of subclinical infections in a high proportion of individuals suggests that these herpesvirus species are well adapted to their marsupial hosts, likely as a result of an extended period of coevolution, and that severe pathology is unlikely to occur in immunocompetent hosts. Studies investigating the effect of these herpesvirus infections in immunocompromised, immunonaïve or unnatural hosts may be required to determine their pathogenecity and characterise the risk they pose to marsupial populations. Herpesviruses identified in threatened marsupial species should be targeted for these further investigations, as the results of such research may be critical in informing the development and management of species recovery programs.