Veterinary Clinical Sciences - Theses
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ItemViscoelastic coagulation changes in dogs with tiger snake envenomation( 2018)Snake venom induced consumption coagulopathy (SVICC) is an important yet poorly described clinical syndrome in the field of veterinary medicine. Publications referencing humans, on the other hand, are numerous in comparison, especially since the establishment of the Australian Snakebite Project. Since the introduction of Australian snake-specific antivenoms, SVICC has become the most common underlying reason for human fatality from snake envenomation in Australia.1 The annual canine snakebite caseload in Australia alone is vast and could be established as a model for the human condition. The overall objective of this study is to extend the scientific literature on SVICC in veterinary medicine, namely the role of thromboelastography (TEG) in tiger snake envenomed dogs. The study assessed the changing clot kinetics of canine whole blood after natural tiger snake envenomation using an established technique called thromboelastography (TEG). Specifically, we will be determining the TEG changes in dogs at several time points: T0 = time of presentation; T1 = 1 hour after antivenom administration; T18 = 18 hours after antivenom administration; and, finally, T24 = 24 hours after antivenom administration. Tiger snake venom caused alterations in TEG parameters, specifically the prolongation of R time (time to initiation of clot formation) during the first 24 hours of envenomation.2 No clinical benefit exists in using TEG over classical coagulation parameters in the identification of SVICC in tiger snake envenomed dogs. Hypercoagulability occurs for 24 hours after envenomation and VetSVICC appears to resolve 18–24 hours after antivenom, which is suggestive of a shorter period to apparent clinical recovery compared to humans, suggesting that VetSVICC may be a unique clinical syndrome. This project is a stepping stone to future research into both SVICC and tiger snake envenomation in veterinary medicine, including establishing an accessible and reliable diagnostic test for SVICC and further delineation of its importance regarding the severity of illness and outcome.
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ItemInvestigation into the relationship between scrotal circumference, body weight, semen characteristics, daughter fertility and genomic breeding values, as well as monitoring behaviour in commercial pasture-based dairy breed natural-service sires( 2018)Use of natural-service sires in the pasture-based dairy industry of south-eastern Australia is common, however, research into their selection and management is sparse. This investigation included a cross-sectional study of the genetic merit of pasture-raised natural-service dairy breed sires and quantified the association between natural-service sire scrotal circumference and their daughter fertility breeding value. Additionally, investigations into the association within breeds between scrotal circumference (as an explanatory variable) and daughter fertility breeding value as the outcome variable in a linear regression model were conducted. And finally, this investigation aimed to monitor bull behaviour, including mounting and serving behaviour, as well as tracking distanced walked. Deoxyribose nucleic acid was submitted for genotyping from two groups of Tasmanian Holstein (n=124) and Jersey (n=85) bull calves to get a set of genomic breeding values. Scrotal circumference and body weight measurements and semen characteristics were recorded at 8 weekly intervals from the age of 6 months to 18 months of age. In addition, an observational study was conducted using collar mounted tri-axial accelerometers and global positioning systems on bulls (n=10) on a commercial pasture-based dairy farm in Tasmania, Australia. The genomic information from natural-service sires was compared to contemporary artificial insemination sires, however a clearly defined association between scrotal circumference and the daughter fertility breeding value could not be elucidated, despite the link in beef breeds. Linear regression quantified the relationship between scrotal circumference and body weight and classification and regression tree analyses were determined the predictive value of scrotal circumference and body weight on semen characteristics. Linear regression showed that 50 kg increase in a Holstein bull’s body weight was associated with a 2.9 (95% CI 2.8 to 3.0) centimetre change in scrotal circumference (P= <0.001). For Jerseys, 50 kg increase in body weight was associated with a 2.4 (95% CI 2.3 to 2.5) centimetre change in scrotal circumference (P= <0.001). Classification and regression tree analysis for Holsteins and Jerseys combined showed that 95% of animals that weighed greater had a scrotal circumference of at least 27 cm had a percent normal sperm score greater than 70%. Using learning algorithms bull behaviour was monitored including grazing (F = 0.86) and walking (F = 0.91) compared with ruminating (F = 0.19) and resting (F = 0.38). However, due to the short, yet explosive nature of the mounting and serving signatures, the algorithm was not able to detect them. Mean distance travelled per day ranged from 12.0km to 6.5km and maximum distance travelled per day of 28.0km to the least maximum distance of 14.6km. This study provides information about the genomic merit of natural-service sires and the relationship between scrotal circumference and daughter fertility, augments information on scrotal circumference and body weight relationships in pasture-raised Holstein and Jersey breed bulls and supports the use of the bull breeding soundness exam to manage the risk for sub-fertility in the dairy industry. Additionally, it was found that walking long distances may contribute to the lameness in dairy natural-service sires.
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ItemThe effects of intravenous fluids on thromboelastrographic variables in dogs( 2018)Intravenous fluid resuscitation plays a fundamental role in treating dogs in haemorrhagic shock, as it can rapidly replenish lost intravascular volume and improve tissue perfusion. However, a consequence of intravenous fluid therapy is interference with haemostasis, which has a detrimental effect to trauma patients that are already haemostatically compromised. In people, intravenous fluid therapy can effect haemostasis and subsequently can increase haemorrhage, transfusion needs and mortality. The effects of intravenous fluids on haemostasis in dogs have not been widely established. More recently, viscoelastic devices like thromboelastography have been used to examine haemostasis. Compared to conventional coagulation testing, viscoelastic devices have the advantages to be able to assess the speed and kinetics of clot formation, clot strength and even the breakdown of the clot. The aim of our study was to determine the effects of intravenous fluids on coagulation in dogs with the use of thromboelastography. The objective of our study was to determine the effect of dilution of canine whole blood with clinically relevant doses of common intravenous fluids on thrombelastographic variables. Our hypothesis was that in vitro dilution of canine whole blood from healthy dogs with intravenous fluids will induce dose-dependent changes in thromboelastographic variables consistent with hypocoagulability. Further, we hypothesized that the characteristics of the fluids, such as its ionic strength and osmolality, will effect thromboelastographic variables in addition to those of dilution alone. The results of our study showed that in vitro dilution of canine whole blood with commonly used intravenous fluids lead to thromboelastographic changes consistent with hypocoagulability in a dose dependent manner. Besides dilution percentage, viscoelastic changes were influenced by fluid characteristics, specifically ionic strength, osmolality and colloidal properties. In our study, 7% hypertonic saline had the most severe effects on coagulation, followed by 20% Mannitol then 3.4% hypertonic saline. Hydroxyethyl starch 130/0.4 had minimal effects on coagulation besides a dilutional effect. The differential effect of fluid characteristics should be taken into consideration when resuscitating dogs with large fluid volumes, but clinical studies are still required to further delineate the importance of different resuscitation fluids and volumes on haemostasis in dogs.
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ItemA pilot study of the seroprevalence of Q fever in cattle, sheep and goats in Victoria( 2018)Q fever is an important public health concern throughout the world and infection can result in debilitating and lifelong illness in some people. It is caused by the bacterium Coxiella burnetii and the most frequent source of infection for humans are domestic ruminants. Over a quarter of human Q fever cases in Victoria, 192 out of 659 (29%) analysed from 1994 to 2013 (Bond et al., 2018), are locally acquired indicating that it is endemic in the state. In addition, outbreaks of human Q fever in Victoria associated with local livestock is causing concern that the incidence of disease is increasing. However, information regarding the amount of infection present in the animal reservoir are lacking in Victoria. The aim of this pilot study was to survey cattle, sheep and goats in Victoria to estimate the individual animal-level, herd-prevalence and within-herd-prevalence of Coxiella burnetii infection. This survey was carried out from February 2015 to May 2017 in Victoria, Australia. Over 1500 blood samples were collected using a two-stage sampling process from farms and abattoirs. Sera were screened using a commercial Q fever ELISA kit for ruminants. True prevalence and intra-class correlation coefficient for each species was estimated using a Bayesian approach to account for known test imperfections. Post-hoc sample size estimates were calculated based on survey results to inform future study planning. Q fever is endemic in domestic ruminants in Victoria at low levels and may even be absent in some parts of the state. Of the herds and flocks that were sampled, 8% (95% confidence interval, 5 to 13%) had at least one animal seropositive for Q fever. Herd-level seropositivity rates were 0% (0, 4.7%) and 8.7% (2.4, 26.8%) for Goulburn Valley and Gippsland cattle respectively, 17.6% (9.6, 30.2%) for sheep and 8.0% (0.2, 25.0%) for goats. The overall pooled true animal-level prevalence was 1.3% (95% HPD, 0.9 to 2%). This was based on true animal-level prevalence of 0% (0, 0%) and 0.4% (0, 3.5%) for cattle in Goulburn Valley and Gippsland respectively, 2.1% (0, 3.7%) for sheep and 1.6% (0, 2.8%) for goats. Although the overall herd- and animal-level prevalence estimates were very low, the individual animal-level prevalence within infected herds (within-herd prevalence) was much higher, ranging from 12 to 19%, by species. Finding a small number of groups of animals with elevated levels of within-herd seroprevalence, whilst not detecting positive results in the rest of the sampled population, indicates that the prevalence of exposure to Coxiella burnetii was geographically uneven, being highly clustered within a small number of farms in Victoria. Post-hoc sample size estimates based on survey results indicate large numbers of farms and animals are required for further studies to confirm this very low rate or the absence of infection in some areas of Victoria. However, a greater priority and more cost-effective approach would be to establish why some farms are at higher risk, and this could be efficiently investigated using a case-control study. The findings of this pilot study present a step forward in understanding the epidemiology of Coxiella burnetii in this region of Australia and point to further areas of investigation and how to conduct such studies.
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ItemThe role of diagnostic imaging in small animal endocrine disease( 2018)The work reported in this thesis aimed to investigate the role of diagnostic imaging in small animal endocrine disease: adrenal gland ultrasound in dogs and thyroid scintigraphy in severely hyperthyroid cats. A prospective study evaluated the effect of the patient’s recumbency position on ultrasound derived adrenal gland measurements in dogs with non-adrenal illness. This research determined that the measurement with the best agreement between lateral and dorsal recumbency position was the caudal pole thickness from a longitudinal image plane. Whereas the measurements from the transverse image plane and the length of the adrenal gland had poorer agreement between recumbency positions. A retrospective review of thyroid scintigraphy findings in severely hyperthyroid cats was compared with the general population of hyperthyroid cats. A greater proportion of the severely hyperthyroid cats demonstrated ectopic thyroid tissue and features which increase the suspicion of thyroid carcinoma. These findings suggest that thyroid scintigraphy is useful in severely hyperthyroid cats and assist with treatment decisions. This work also evaluated the role of thyroid scintigraphy in the calculation of an individualised compared to a standard radioiodine dose. The treatment outcome was assessed by the initial post treatment total T4 and found fewer cats receiving a standard radioiodine dose had a total T4 below the reference range. This finding indicates that further evaluation of radioiodine dosing regime is warranted in severely hyperthyroid cats. Thus, the ultrasound assessment of dogs with non-adrenal gland illness has been simplified for all veterinarians including those with less ultrasound experience as the current reference ranges of ultrasound derived adrenal gland measurements were validated and there is flexibility of patient recumbency during the ultrasound examination. Also, this work has contributed to the knowledge of the role of thyroid scintigraphy in both the diagnosis and treatment of severely hyperthyroid cats.
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ItemEvaluation of tibiotarsal transarticular immobilization techniques and kinematic study of the gastrocnemius muscle-tendon unit in dogs( 2018)The common calcaneal tendon is a complex muscle-tendon system that regulates flexion/extension of the tibiotarsal joint motion as well as the phalanges. Common calcaneal tendon injury is not uncommon, and two types of injuries are recognized: acute or chronic. Acute injuries are usually related to trauma by a sharp object, transecting skin and underlying structures, including tendons. No definitive causes of chronic injury have been identified, but middle age, large-breed dogs are more predisposed to be affected. The treatment of common calcaneal tendon injury consists of debridement, anastomosis and temporary tibiotarsal joint immobilization during tendon healing. Acute traumatic common calcaneal tendon injury is managed in a very similar way for each patient. Several types of immobilization technique have been described, however, no optimal immobilization technique that neutralizes tension in the common calcaneal tendon has been identified. Numerous biomechanical studies of common calcaneal tendon repairs are reported in human and animal models. In human patients, early controlled motion minimizes various complications, resulting in better outcomes. However, there is no gold standard postoperative protocol for veterinary patients. It can be problematic in veterinary patients to control patient activity and have good client and patient compliance. In this research project, six tibiotarsal transarticular fixation methods were evaluated, and a kinematic evaluation of the gastrocnemius tendon was performed at various femorotibial and tibiotarsal joint angle combinations. These data will help inform development of an optimal immobilization method during healing of common calcaneal tendon injury in dogs.
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ItemA comparison of the incidence of apnoea following induction of anaesthesia with propofol or alfaxalone in dogs( 2018)Animals are often given combinations of drugs that produce sedation prior to the use of agents that induce general anaesthesia. Following sedation, induction of general anaesthesia can cause a period of apnoea (cessation of ventilation) which is commonly referred to as post-induction apnoea. If post-induction apnoea persists it can pose significant risk to animals undergoing anaesthesia. This thesis examines the effect of intramuscular premedication drugs acepromazine and dexmedetomidine combined with methadone, commonly used to produce sedation in canines prior to anaesthesia, and the effect of the anaesthetic induction drugs propofol and alfaxalone on the incidence and duration of post-induction apnoea in healthy dogs. In addition, the effect of the rate of administration of propofol and alfaxalone on the incidence and duration of post-induction apnoea in healthy dogs is also described. Prospective, randomised clinical trials identified no difference in effect of the premedication drugs acepromazine and dexmedetomidine on post-induction apnoea when using propofol or alfaxalone. The results of the trials conducted also did not identify a difference in incidence or duration of post-induction apnoea following either propofol or alfaxalone; however, a significant effect of rate of administration of these drugs on incidence and duration of post-induction apnoea was detected. The duration of apnoea following propofol or alfaxalone was significantly longer when these drugs were given rapidly. Based on these findings, propofol and alfaxalone cause significant post-induction apnoea and the rate of administration of both drugs should be reduced where possible. The incidence and duration of apnoea does not appear to be influenced by the use of acepromazine or dexmedetomidine in combination with methadone for premedication. Monitoring of respiration is recommended when using these premedication and induction agent combinations.
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ItemMeasurement of TNF-α and IL-6 in canine abdominal effusions using enzyme linked immunosorbent assays( 2018)The importance of biomarker research depends on the underlying validity of the data. The use of immunoassays for quantifying biomarkers in complex biological matrices is widely reported. Interfering factors within complex biological matrices are also widely reported and have the potential to affect the accuracy of immunoassay results. Biomarkers in sepsis are an evolving field in veterinary medicine and there is currently a scarcity of reports where biomarkers have been evaluated in body cavity effusions in dogs. This project aimed to evaluate whether biomarkers IL-6 and TNF-α can be reliably measured in abdominal cavity effusions and also aimed to report pilot information on concentrations of these cytokines in septic and non-septic canine abdominal effusions. Material and methods A feasibility study was conducted to determine the performance of plasma- validated ELISA assays for IL-6 and TNF-α, when analysing canine abdominal effusions. Performance was assessed using the following criteria; parallelism, selectivity and assay linearity. In addition to this, storage stability of the samples was assessed. Serially diluting an inflammatory abdominal effusion sample and assaying each dilution for IL-6 and TNF-α was used to determine parallelism. The results of observed and expected concentrations of the samples were subsequently compared. Known quantities of reference standard for IL-6 and TNF-α of variable concentrations (low, medium and high) were also added to inflammatory and non-inflammatory canine abdominal effusions. Recovery of the recombinant cytokines from the samples was used to assess selectivity and assay linearity was determined by dilution (serial and 2 direct) of these samples. In addition to the feasibility study, a pilot study was performed to evaluate the concentrations of endogenous IL-6 and TNF-α within canine abdominal effusions of inflammatory and non-inflammatory aetiology using the same ELISA assays. Abdominal effusions were collected from clinical cases of dogs presenting with abdominal disease resulting in varying degrees of inflammation. The effusions were assessed for the presence of inflammation or sepsis and stored at -70°C until later measurement of IL-6 and TNF-α using commercial ELISA assays. Plasma samples were collected from these cases at the same time as the abdominal effusions and cytokine concentration were measured at the same time after storage, under the same conditions. Results The ELISAs used for this study did not pass the feasibility study when assessed using the criteria selectivity and assay linearity. Parallelism can be achieved in a highly inflammatory sample and further samples will need to be assessed in order to fully satisfy this criterion. The performance of the IL-6 ELISA was slightly better than TNF- α with respect to selectivity and assay linearity and so could be considered as a potential assay, but refinement of assay techniques would need to be explored further. In addition to this, there was evidence of storage stability issues of endogenous cytokines in the samples, which hampered any ongoing analysis over the time period.
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ItemInfluence of retractor type and position on thoracoscopic-assisted pulmonary surgery in dogs( 2018)Thoracotomy is performed frequently in dogs for the purposes of exploration of the thorax, lung lobectomy, correction of vascular ring anomalies and patent ductus arteriosus, pericardiectomy, thoracic duct ligation, biopsy and resection of mediastinal and pleural masses and removal of foreign bodies from within the pleural space, intrathoracic oesophagus and the lower respiratory tract. Persistent post-thoracotomy pain is reported frequently by human patients characterised by discomfort and altered sensation in the skin adjacent to the surgical site. Multiple surgical techniques have been developed in an attempt to reduce the morbidity of these procedures. Minimally invasive surgical techniques have been a significant step towards this goal. A significant limitation of minimally invasive surgery is the loss of tactile feedback and video-assisted techniques which utilise smaller incision, permitting the introduction of the surgeon’s hand or fingers to the thorax have been developed to overcome these limitations. These techniques have recently been introduced for veterinary patients (Chambers and others 2012, Gower and Mayhew 2011a, Laksito and others 2010b, 2011, Wormser and others 2014). Both traditional and video or thoracoscopic-assisted techniques require the use of tissue retractors, typically placed in an intercostal position. Access is afforded by the forceful retraction of soft tissues such as the intercostal muscles and ribs. Studies in both animals and humans have demonstrated detrimental soft tissue changes associated with such retraction including direct and ischaemic damage to the soft tissues adjacent to the retraction device. The present study examines several aspects of thoracoscopic-assisted pulmonary surgery in dogs including the effect on blood flow in the intercostal musculature and nerve conduction in the intercostal nerves associated with two different retraction modalities. Additionally, the influence of assisted port location and thoracic conformation on access to and delivery of pulmonary tissues for the purposes of complete or partial lung lobectomy was assessed. Force, contact area and pressure were compared and related to intramuscular pressure, perfusion, oxygen indices, nerve conduction and histologic change in dogs undergoing simultaneous controlled thoracotomy incisions. The novel retractor resulted in lower pressure and improved oxygenation in adjacent tissues compared to mechanical retraction which may translate clinically into reduced post-operative morbidity. For all lobes except the accessory lung lobe, the exposure provided by the reported thoracoscopic-assisted approach was considered adequate for complete or partial lung lobectomy. The cranial and caudal portions of the left cranial lung lobe and the right middle lung lobe were best exposed with the assisted portal in the middle dorso-ventral third of the thoracic wall at the fourth intercostal space of the ipsilateral side in both breeds. The right cranial lung lobe was best exposed with the assisted portal positioned in the middle third of the fourth intercostal space in kelpies but the sixth intercostal space in greyhounds. The right caudal lung lobe was best exposed when the assisted portal was positioned in the ventral third of the fourth intercostal space in the kelpie but in the middle third of the sixth intercostal space in the greyhound. The described thoracoscopic-assisted technique is a practical method for exposure of the lobes of the lung, other than the accessory lobe, for partial lung lobectomy in the dog. The portals described also allow the introduction of a linear stapler for the purpose of complete lung lobectomy.
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ItemMetal endoprostheses for limb salvage surgery in dogs with distal radial osteosarcoma: evaluation of first and second generation metal endoprostheses and investigation of a novel endoprosthesis( 2017)Osteosarcoma (OSA) is the most commonly diagnosed primary bone tumour in dogs, usually affecting middle-aged, large breed dogs. The standard of care surgical treatment for local tumour control in dogs with osteosarcoma is limb amputation; however limb-sparing surgery is gaining wider acceptance as an alternative surgical treatment. All limb sparing techniques show high complication rates, including infection, construct failure or fracture and local recurrence. Metal endoprosthesis (EN) limb-sparing surgery was developed to overcome limitations of other techniques, including access to specialised equipment and facilities such as radiation therapy or bone bank facilities. The first generation of metal EN (GEN1) was shown to be biomechanically superior, but not clinically different to the cortical allograft. A second generation metal EN (GEN2) was developed but biomechanical studies and clinical outcomes have not been reported other than in single case reports. The first component of this thesis is a multi-institutional retrospective case series that evaluated surgical and oncologic outcomes for dogs treated with GEN1 or GEN2 for OSA of the distal radius. Records from 45 dogs with distal radial OSA were examined; 28 dogs received GEN1 and 17 dogs received GEN2. One or multiple complications occurred in 43 dogs (96%, 14 minor, 29 major) including 35 with infection (78%), 16 with implant-related complication (36%) and 11 with local recurrence (24%). This study showed no significant difference in case (surgical or oncologic) outcomes between dogs receiving GEN1 and GEN2 endoprosthesis for limb-sparing surgery of the distal radius. The frequency of complications, including infection and those implant-related, remains unacceptably high for both generations of endoprosthesis. Further refinement of the endoprosthesis or re-evaluation of the surgical technique for implantation of the endoprosthesis is indicated. A finite element (FE) model of the canine forelimb has been designed by a multi-disciplinary team from Colorado State University. Evaluation of GEN2 in the FE model predicted stresses in the proximal radius that exceeded the fatigue limit and yield stress of 316L stainless steel; the predicted stresses of GEN2 are too high for sustained performance. An engineering specific approach was taken to design a novel EN and evaluation in the FE model resulted in 50% reduction in peak stresses in the radial screws compared to GEN2 in the FE model. The second component of this thesis is evaluation of the suitability of the novel EN for clinical use. The novel EN prototypes were manufactured using three-dimensional printing (3DP) in plastic and stainless steel. Three size variations of the novel EN were designed using a computer-aided design (CAD) program and implanted into large breed cadaver radii. There was a large variation in radius morphology between and within large breeds; making the novel EN unlikely to be suitable as an off the shelf implant. The most appropriate application of the novel EN would be via rapid prototyping based on an individual’s computed tomography scan. This thesis highlights the difficulties associated with limb sparing surgery in veterinary surgery. The currently available procedures provide an alternative for pet-owners that are averse to amputation. However, pet-owners must be aware of the high complication frequencies associated with the techniques. Once refined; the novel EN has potential to decrease implant-related complication rates, however the infection rates are likely to remain high.