Veterinary Science Collected Works - Theses
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ItemUse of behavioural signs for riskbased prevention of catastrophic breakdown in racehorses( 2020)Bone and joint injuries in Thoroughbred racehorses typically originate in areas of intense loading. Despite the increasing understanding regarding the pathogenesis of bone fatigue, early detection prior to fatigue fracture is difficult. This thesis focuses on understanding equine behaviour and its potential to reflect orthopaedic pain to assist in the early identification of horses at risk of injury. Previous research suggests an association between facial expression and the presence of equine lameness. In cattle, motion sensors have been validated to record recumbency behaviour used to detect disease without the need for continuous observation. This thesis aimed to investigate monitoring of behavioural patterns as predictors of injury in racehorses. In the first study, Thoroughbred racehorses were monitored at rest with motion sensors placed on forelimbs. Sensor data was collected, and an algorithm developed to identify certain behaviours. Algorithms were validated through video observation and calculation of algorithm sensitivity and specificity. There was excellent agreement for standing, lying, and for stepping behaviour patterns suggesting potential for long term, objective, remote monitoring of horses in the stable environments. In the second study, previously validated facial grimace scales were used to score pain from photographs of Thoroughbreds, captured from video recordings during trot up examinations. This method demonstrated horses with moderate mouth strain (HGS) and tense and extended upper lip (FEReq) were associated with horses less likely to be lame. Exposed sclera was associated with lameness in hand, at the trot. Cohen's kappa was used to measure the proportion of agreement between raters, with behaviours scored to more than two categories the kappa was ordinal weighted. Mean inter observer agreement was moderate, and the sum of facial scores showed no difference between lame and sound horses. There were few associations between lameness status and facial predictors, limiting the potential use of facial expression for prediction of orthopaedic pain during pre-race lameness examinations. In conclusion, motion sensors are sensitive to detect horse movements and have potential use in longitudinal monitoring of horse behaviour. Future research in this area includes prediction of behavioural indicators of musculoskeletal pain in racehorses that could contribute to the development of a risk-based injury prevention model. The facial grimace scales had limited ability to differentiate lame from ‘sound’ horses in this cohort of racehorses. External factors associated with racehorse management, including environmental stress, may be one reason facial grimace scales are not effective for the recognition of subtle lameness in this cohort.
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ItemLaparoscopic & Laparoscopically-Assisted Surgery in Rabbits: Comparison of Isobaric and Insufflated Laparoscopic Techniques to Open Laparotomy( 2019)The use of laparoscopic surgery for routine procedures such as ovariohysterectomy has been well described for dogs and is common in humans. Rabbits have been previously used as models for human laparoscopic surgery and training models for paediatric surgery, however reported use of clinical laparoscopy in rabbits is rare. There are concerns for use of laparoscopic surgery in rabbits due to the effects of the insufflation on ventilation and the risk of increased morbidity from the insufflation contributing to gastrointestinal stasis, a common and life-threatening complication of any surgery in rabbits. This study is designed to quantify and characterise the changes in the postoperative morbidity between open, insufflated and isobaric laparoscopy in healthy adult rabbits. The hypotheses were that use of isobaric laparoscopy will decrease the morbidity of ovariohysterectomy procedures compared to open and insufflated ovariohysterectomy at the expense of increased surgical time. Various investigations were performed over the research project, including a technical viability cadaveric study, a study describing the effects of isobaric and insufflated pneumoperitoneum on ventilatory capability and abdominal dimensions, a study describing the clinical implementation of a Rabbit Grimace Pain score and Behavioural Pain Score in the detection of postoperative pain, and a clinical trial assessing the effects of both laparoscopy methods and comparing them with open laparotomy for ovariohysterectomy. The overall findings of the study support the implementation of isobaric laparoscopy in the rabbit, and the use of laparoscopy in general as a method of reducing postoperative morbidity compared with equivalent laparotomy approaches.
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ItemAn investigation into the role Toxoplasma gondii may play in the health of the southern brown bandicoot (Isoodon obesulus obesulus) and an assessment of environmental contamination with T. gondii( 2020)The southern brown bandicoot (Isoodon obesulus obesulus), a small, ground-dwelling marsupial, is listed as ‘endangered’ under the Australian Environment Protection and Biodiversity Conservation Act 1999. While many factors contributing to population decline are understood, in particular predation and loss of high-quality, connected habitat, there is a lack of knowledge about other threatening processes, including disease, which has contributed to declines in other small mammal species. Toxoplasma gondii, a protozoan intracellular parasite, excreted into the environment by cats, has been shown to cause clinical disease, including death, in many small and medium sized captive and free-ranging marsupials, including the eastern barred bandicoot (Perameles gunnii). Little is known of its effect on southern brown bandicoot populations. This study aimed to investigate the significance of T. gondii to the health of southern brown bandicoot populations on the northern hinterland of Western Port, Victoria and methods of predicting probability of infection with environmental T. gondii. A series of necropsies was performed on 33 southern brown bandicoots collected opportunistically over a five-year period. The causes of death were identified as motor vehicle trauma (22); predation (4); ejected pouch young (2); drowning (1); pyometra (1); possible toxicity and stomach bloating through lentil ingestion (1) and unknown (2). Real-time qPCR was performed on tissues from 30 cases, all of which were negative for the presence of T. gondii DNA. A range of helminths and ectoparasites were collected and identified, most of which had been previously been reported in this species. However, a metastrongyloid helminth species, found by histopathology in the lungs, is reported for the first time in a southern brown bandicoot. To assess environmental contamination with T. gondii, two sites with different cat densities were compared. Seroprevalence of antibodies to T. gondii (n=24) using the Modified Agglutination Technique was performed on trapped southern brown bandicoots. No evidence of infection with T. gondii was found at either site. Molecular (qPCR) methods were used to measure T. gondii oocyst presence in soil samples (n= 594) and prevalence of T. gondii in tissues of rabbits (n=118) and mice (n=267). All tests were negative across both sites except for the presence of T. gondii in one rabbit (prevalence 0.85%). These results suggest that rabbits and mice may have the potential to be reliable sentinel species and inform conservation management of the probability of infection with T. gondii in small marsupials. The results from this study are consistent with the concept that opportunistic necropsy is a valuable strategy for passive disease and cause of death surveillance in native wildlife. No evidence was found that T. gondii was impacting the health of southern brown bandicoots, however, further longitudinal health surveys are necessary to determine the true prevalence of disease and causes of mortality. Further studies are recommended to confirm the effectiveness of mice and rabbits as potential sentinel species in a range of ecosystems, including those environments which have higher levels of contamination with T. gondii.
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ItemLeptospirosis prevalence and vaccination practices in South-West Victorian dairy herds( 2019)While previous studies of Leptospira Hardjo in Victoria demonstrated a relatively high prevalence of exposure in both cattle (40%; Milner et al. 1980) and humans (22%; Sutherland 1988) these estimates need to be revised since they were made more than 30 years ago and leptospirosis vaccination programmes are now commonplace on Victorian dairy farms. This was a cross-sectional study to estimate the prevalence of Leptospira borgpetersenii sv Hardjo and Leptospira interrogans sv Pomona in dairy herds in South-Western Victoria. Fifty-three herds were enrolled into the study. Herd managers were asked to present 15 late-lactation cows that had fertility issues (cows that had not conceived or had delayed calving to conception intervals). Furosemide 500 mg was injected into the tail vein of eligible cows and a mid-stream urine sample of the second voiding collected to increase the likelihood of sampling leptospira .At the time of each herd visit a questionnaire was administered to herd managers asking them to provide details of methods used for controlling leptospirosis, including vaccination. Urine samples were pooled at the herd level and tested for leptospira spp. using qPCR. Pooled samples were then tested individually and samples that were positive, were tested for Leptospira Hardjo and Leptospira Pomona using qPCR. Three of the 53 pooled urine samples returned a positive result. The leptospira positive pools returned a minimum of three positive individual cow urine samples. Testing of individual cow urine samples identified an additional positive herd (with one weak positive and one inconclusive result), giving an apparent prevalence of approximately 8 (95% CI 1 to 13) leptospira-positive herds per 100 herds at risk. Based on the 53 completed questionnaires, leptospirosis vaccination programs were non-compliant with label directions in 35 out of 52 vaccinated herds: 67 (95% CI 54 to 78) out of 100 herds that routinely vaccinate for leptospirosis were doing so incorrectly. Of the 53 herds that took part in this study, only one herd was completely unvaccinated. Based on the findings from this study, and assuming the herds that took part in this study were an unbiased sample of the dairy herd population at risk, we estimate that close to one out of 10 dairy farms in South-Western Victoria are leptospirosis positive. While most herds are vaccinating for leptospirosis, most are doing so incorrectly. We conclude that herd managers need to be better educated regarding leptospirosis vaccination programs.
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ItemWelfare implications of castration and disbudding procedures on calves( 2020)Castration and disbudding are necessary husbandry practices commonly performed in farms which have the potential to induce stress and pain if not managed correctly. Depending on the severity of a stressor, potential stress responses can suppress immune function, lower resistance to disease-causing factors, contribute to, and result in, reduced animal welfare. Scientific literature is discordant on what recommendations should be transferred to farmers and practitioners regarding the preferred age to castrate and disbud calves. This lack of scientific support to guide recommendations is even more noticeable in suckler beef calves, since most of the disbudding studies have used dairy calves and most of castration studies have used dairy calves or calves older than 6-mo-old. In this thesis, a series of studies were conducted to investigate: a) the age-related differences in plasma cortisol, acute phase protein, metabolite concentrations, haematological variables, behaviour and performance of suckler beef calves in response to Burdizzo castration; b) the effect of sex, breed and age on horn bud size of dairy and beef calves at disbudding; c) the relationship between age and horn bud size of dairy and beef calves at disbudding; d) the horn bud growth in Holstein Friesian calves. Results indicate that Burdizzo castration caused significant stress in 2.5- and 5.0-mo-old calves, characterized by the increase in plasma cortisol concentrations, scrotal swelling, and abnormal behaviours observed after treatment. These responses were reduced by castrating calves at younger age. A secondary stress response was observed, which was greater in older castrated calves, suggesting that calves castrated at older ages have a prolonged overall stress response, compared to younger calves. There was no effect of castration on haematology profiles, haptoglobin, metabolites, body temperature and growth performance. Thus, if calves are to be castrated without analgesia or anaesthesia, then it would be preferable to do this at 2.5-mo-old rather than later, such as 5.0-mo-old, in order to minimize the physiological stress, scrotal swelling and pain-related behaviours associated with Burdizzo castration. Horn bud size at time of disbudding, irrespective of calf sex, was greater in Holstein-Friesian calves than Charolais, Simmental and Limousin calves. These results suggest that horn bud develop differently in beef calves compared with dairy breed calves. In addition, the relationship between age and horn bud size was very weak in all breeds studied with no difference due to calf sex. This means that the age of the calf is not a good predictor of the horn bud size. Therefore, the age of the calves is not a good parameter to guide recommendations on the best age to disbud calves and use of pain relief due to the great variation in horn bud size within and between breeds. The findings of this thesis will have implications for the welfare of cattle in relation to best recommendations regarding the age at castration of suckler beef calves and disbudding of dairy and suckler beef calves.
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ItemCoagulation factor activity patterns in venom-induced consumption coagulopathy from naturally occurring tiger snake (Notechis scutatus) envenomation in dogs( 2020)Snake venom-induced consumption coagulopathy (VICC) is an important syndrome resulting from snake envenomation. The prothrombin activator notecarin D is responsible for this coagulopathy in tiger snake (Notechis scutatus) envenomation. In dogs, the presence of this coagulopathy is used to assist with the diagnosis of snake envenomation and, in some cases, can produce clinical signs associated with a coagulopathic envenoming. There are subtle differences in this syndrome between dogs and people, particularly concerning the development of clinical signs. Chapter two reviews tiger snake envenomation and the consequent VICC in Australian dogs with comparisons to human literature. The VICC syndrome between the two species share many clinical similarities; the key difference lies in the significance of clinical haemorrhage in people when compared with dogs. A brief overview of coagulation and coagulometry is provided. Chapter three is a prospective observational cohort study characterising the coagulation factor activity patterns in VICC from naturally occurring tiger snake envenomation in dogs. The changes in coagulation factors in a study cohort of tiger snake envenomed dogs were compared to a healthy control cohort. Fibrinogen, factor V and factor VIII were identified as the most consumed factors and displayed the fastest recovery to control values. Tests of coagulation times (i.e., prothrombin time and activated partial thromboplastin time) were similarly affected. Additionally, higher serum tiger snake venom concentrations were associated with greater reductions in factors II, V and VIII, and greater prolongations in both coagulation times. The elucidation of the consumption and recovery pattern of coagulation factors in dogs, contrasted with that of people, provides insight into the underlying mechanisms of tiger snake VICC and its treatment. This information can be used for further diagnostic and therapeutic endeavours.
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ItemLuxation following press-fit cementless total hip replacement in dogs: Novel techniques for predicting and treating post-operative luxation( 2019)The objective of this thesis is to investigate the relationship between coxofemoral geometry and luxation of total hip replacements (THR) in dogs. This research question was explored in two parts. Examination of the relevant literature demonstrates that increased pre-operative soft tissue laxity is a risk factor for prosthesis luxation in dogs. However, there is little information pertaining to changes in this soft tissue tension in dogs after surgery and the impact this change may have on prosthesis stability. The first part of the thesis explores the association between radiographic measures of pre-operative soft tissue laxity, or offset, and the occurrence of luxation following total hip replacement. The offset measurements were validated in a pilot study, where ventrodorsal pelvic radiographs were assessed in a dog placed in varying degrees of pelvic rotation. Pre-operative and post-operative offset measurements, as well as measures of prosthesis orientation were made for dogs with confirmed dorsal luxation and compared with those of randomly assigned dogs with uneventful post-operative recovery using a case control study. Univariate generalised linear models were used to identify variables of interest and these were assessed in multivariate logistic models. Global offset of the hip was reduced after surgery in both groups, however, reduction was greater in the luxation group (17.7%) compared to the control group (7.4%) and was associated with an increasing odds of luxation. An open orientation of the acetabular cup was also positively associated with luxation. These results indicate that large changes in soft tissue tension after surgery may be a risk factor for luxation. In the second part of the study, a novel technique for surgical revision of luxated total hip replacements was explored. A triple pelvic osteotomy (TPO) was performed in 17 dogs with dorsal hip luxation and the efficacy of this procedure in preventing luxation recurrence, by altering the geometry of the acetabulum, was reported in a retrospective case series. Measurements of acetabular cup orientation were made from pre- and post-operative radiographs and compared using a parried t-test. The revision TPO was successful in preventing reluxation in fourteen cases and an excellent or good clinical outcome was reported in 12 cases. Ventral luxation occurred in three dogs due to over-rotation of the hemi-pelvis. The TPO significantly reduced the angle of lateral opening by 23.0o and increased the version angle of the acetabular cup by 9.0o. The results of this study show that the TPO is an effective procedure for managing THR luxation with retention of implants, however, careful patient selection is recommended to avoid subsequent ventral luxation. In the closing chapter, the challenges of managing surgical cases with significant pre-operative hip laxity are discussed and potential solutions are explored. Limitations of the studies presented in this thesis are also explored and future directions for research are proposed.
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ItemA study into the genotypes of Escherichia coli from pyometra affected dogs( 2019)Pyometra is one of the most common reproductive diseases in female intact dogs. It affects nearly 25% of all intact female dogs before they reach 10 years of age. This disease not only affects the animal’s health but also its breeding value. The predominant pathogen that has been isolated from dogs with pyometra is Escherichia coli (E. coli). The research described in this thesis focused on characterising the particular strains found in dogs affected by pyometra and comparing them with those found in the rectum of control dogs. The objectives were to identify differences regarding the genotype, the presence of genes transcribing for uropathogenic virulence factors (UVF) and the bacteria’s abilities to form biofilms. The initial aim of investigating differences between bacteria isolated from young and old pyometra patients was hindered by the limited availability of E. coli strains from young dogs. To achieve these aims uterine, vaginal and rectal samples were collected from 32 pyometra patients and the patients’ age was recorded. Rectal samples were collected from 45 clinically healthy dogs to serve as controls. Samples were analysed by polymerase chain reactions for genotyping by Clermont’s scheme and evaluation of UVF gene presence. A subset of samples was further investigated to analyse their biofilm forming potentials using crystal violet assays. Finally, the ability of biofilm producing bacteria to withstand antimicrobial treatment was evaluated using assays to determine the minimum inhibitory concentration and time-kill curve studies. These investigations demonstrated that there is a significantly different UVF gene profile in E. coli isolated from pyometra patients when compared to control dogs. In contrast, there were only few differences between the uterine, vaginal and rectal samples taken from the same dogs. Similarly, little difference was detected between phylogenetic groups with the majority of all samples being classified as B2. Isolates with strong biofilm forming potential were only identified from those collected from pyometra patients but not control dogs and they were subsequently shown to be more resistant to antimicrobials. These studies have shown that there are major differences between the E. coli strains present during pyometra and those present as part of the normal microflora in the intestinal tract. It is also the first time that the biofilm forming potential was evaluated for bacteria involved in pyometra. It becomes apparent that care must be taken in the medical treatment of pyometra patients to consider the impact of biofilms on their efficacy.
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ItemInvestigation into the Morphology of the Canine Sacrum and its Relationships with Selected Structures of the Vertebral Column and the Hind Limb( 2019)In dogs, the sacrum consists of three fused vertebrae (Evans & De Lahunta, 2013) and recently the population of greyhounds in Victoria, Australia have shown a remarkably high incidence of sacrocaudal fusion in which the sacrum consists of four fused vertebra (Oheida, Philip, Yen, & Davies, 2016). Scientific data and the available literature regarding how the occurrence of sacrocaudal fusion might influence the morphology of other parts of the locomotory system in dogs is not clear enough to explain why sacrocaudal fusion appears to be so prevalent in the Victorian greyhound population. This study set out to explore the hypothesis that there are measurable differences in the morphology of the sacrum (S. Weight, S. Length, and S. Width) between greyhounds with standard (3 fused vertebrae) and those with different types of fused sacra (4 fused vertebrae, Type B, C, and D). Also, it was hypothesised that there is an association between the sex and body mass of the greyhounds and morphology of the sacrum (S. Weight, S. length, and S. Width). In addition, this study included an exploration into the influence of sacrocaudal fusion on the morphology of related anatomical structures within the spine such as the L.7 vertebra, and selected bones in hind limbs such as the calcaneus, talus, and patella. The sacra were collected from 171 greyhounds and classified using two systems. For the first system, sacra were classified based on the number of fused vertebrae and the type of fusion into four types: Type A (standard sacra), Type B (complete fusion between the transverse processes and between the bodies of the S3 and Ca1 vertebrae), Type C (fusion only between the transverse processes of the S3 and Ca1 vertebrae), and Type D (fusion only between the bodies of the S3 and Ca1 vertebrae). For the second classification system, sacra were classified based on the presence, reduction, or absence of the median sacral crest between the spinous processes of the S1 and S2 vertebrae into the following three types: Type F (a complete fusion or crest), Type R (reduction in the height of the crest between successive spinous processes), and Type N (absence of the crest). The length, width, and weight of sacra, calcanei, tali and patellae were recorded and compared between the greyhounds with standard and fused sacra. Also, the length of the L.7 vertebra and the angle of the lumbosacral junction and the angle of the spinous process of the 1st sacral vertebra were compared between the greyhounds with standard and fused sacra. There were variable numbers of the population in various chapters because some bones were too difficult to measure or because of breakage of bones during processing. The exact sample numbers are indicated in each table illustrating the results. The results of the studies showed that there was an increase in the convexity of the curvature of the pelvic surface of the sacrum and an increase in the roughness of the articular surface of the sacral wing in association with the occurrence of sacrocaudal fusion. Sacrocaudal fusion was found in 71 out of 171 greyhounds (41%). Overall, the mean weight, length, and width of the fused sacra were found to be significantly greater (P < 0.01) than standard sacra. Among the fused sacra, 13.5% (23/71) were Type B, 21.1% (36/71) Type C, and 6.4% (11/71) Type D. Type B sacra (complete fusion) were the heaviest (P <0.001), broadest (P <0.001), and longest (P <0.001) sacra compared to Type A, C or D sacra. Regarding standard and different types of fused sacra, there was no association between the sex, body mass and the occurrence of sacrocaudal fusion. In addition, different scenarios were suggested for the evolution of sacrocaudal fusion in the greyhound. The first scenario was termed “Continuous Dependent Sacrocaudal Fusion”, in which it was proposed that fusion occurred first between the S3 and Ca1 vertebral bodies, followed by the occurrence of fusion (Type C), with a final result of complete fusion (Type B). The second scenario was termed “Continuous Independent Sacrocaudal Fusion”, in which the sacrum might change from Type A to either Type C or D, and then further evolve into Type B (complete fusion). The third proposed scenario was termed “Non-continuous Independent Sacrocaudal Fusion”, in which a sacrum may evolve directly from Type A (standard) to be Type B, C or D without going through the possible sequences assumed in the first or second scenarios. The reduction (R) or absence (N) of the median sacral crest between the spinous processes of the S1 and S2 vertebrae, which has been observed in association with the occurrence of sacrocaudal fusion, allowed us to suggest this new classification of sacra in greyhounds. This classification divided sacra into three different types (F, R, and N) and the percentage of each was found to be significantly different between standard and fused sacra (P <0.001) with the fused sacra more commonly showing the N type, and not associated with sex or body mass. In addition, the angle of the spinous process of the 1st sacral vertebrae of sacra with median crest type N was statistically significantly less (more upright) than those in sacra with median crest type F (P <0.042). Investigating the morphology of the L.7 vertebra as an anatomical structure articulating directly with the sacrum and lumbosacral junction, showed that the L.7 length was significantly (P ≤ .008) longer and the angle of the lumbosacral junction in greyhounds with fused sacra was significantly increased (P <0.028) in dogs with sacrocaudal fusion compared with those with standard sacra and this variation was not associated with sex (P <0.765) or body mass (P <0.802). The results showed that the right and left calcanei, tali, and patellae in greyhounds with standard and fused sacra were anatomically similar. Among all greyhounds, asymmetry between some of measurements was found, including in the width of the calcaneus (P <0.009) and the talus (P <0.025) and the length of the calcaneus (P <0.001). Measurements were higher in those bones from left hind limbs. Studying specifically the greyhounds with standard sacra also showed asymmetry in the length of the calcaneus (P <0.008) and again those calcanei from left hind limbs (L.C.L) were longer than those from right hind limbs (R.C.L). For greyhounds with fused sacra, asymmetry was found in the width of the talus (P <0.024) and again those of left hind limbs were wider than those from right hind limbs. Regarding the influence of sacrocaudal fusion on bones, there were no significant differences in the mean of measurements in bones between greyhounds with standard and those with fused sacra except for the mass of the right (M.R.C, P <0.003) and left (M.L.C, P <0.006) calcaneus. Also, the measurements of these limb bones from greyhounds with fused sacra were heavier than those with standard sacra. This thesis provides quantitative data about the occurrence of sacrocaudal fusion and is the first study to investigate the morphological anatomy of the two types of sacrum: standard or fused, as well as selected bones in the vertebral column and hind limbs of greyhounds, such as the L.7 vertebra, calcaneus, talus, and patella. In summary, sacrocaudal fusion in greyhounds was associated with a change in the morphology of the sacrum, which included an increased angle of the spinous process in the 1st sacral vertebra, a reduction or absence of the median sacral crest between the spinous processes of the S1 and S2 vertebrae, and changes in related structures, such as an increase in the length of the L.7 vertebra and angle of the lumbosacral junction. Furthermore, it seems that sacrocaudal fusion has a type of influence on certain hind limbs bones such as the mass of the right and left calcanei. These variations in the anatomical features of the sacrum between dogs with or without sacrocaudal fusion may influence the effect of forces applied to the sacral region and also the incidence of injuries. In conclusion understanding the morphological variations of different types of sacra, in addition to the data provided by this thesis, is establishing a solid base for further research, which might help to explain why sacrocaudal fusion is so common in the Victorian greyhound racing population. Overall, this work provides an anatomical foundation for understanding the function of the sacrum in greyhounds and highlights how investigation into the sacral anatomy and related structures of the greyhound body may further the current understanding of dog locomotion.
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ItemAssessment of treatment outcomes and symmetric dimethylarginine in hyperthyroid cats treated with a fixed dose of radioiodine( 2019)Background: Hyperthyroidism and chronic kidney disease (CKD) are common in geriatric cats and often occur concurrently. Among other effects, hyperthyroidism causes protein catabolism and increases renal blood flow and the glomerular filtration rate (GFR). These effects render traditional renal markers insensitive for the detection of CKD in cats with uncontrolled hyperthyroidism. Early identification of occult CKD may influence the prognosis, monitoring and therapy of hyperthyroidism or CKD. Symmetric dimethylarginine (SDMA) is a new serum renal biomarker that is stable, easily measured and has been recently validated for use in cats. SDMA correlates well with GFR and is not affected by muscle mass. SDMA is more sensitive than serum creatinine in detecting early CKD in non-hyperthyroid cats, but our understanding of its performance in hyperthyroid cats is in its infancy. In Australia, the gold standard treatment for cats with benign hyperthyroidism (i.e. thyroid hyperplasia or adenoma) is a fixed dose of orally administered radioiodine, regardless of the serum total thyroxine (TT4) concentration at the time of diagnosis. The development of iatrogenic hypothyroidism after radioiodine treatment is detrimental to renal function and may negatively affect long-term survival. As a result, the goal of radioiodine treatment is to maximise the number of cats that achieve euthyroidism while limiting the development of hypothyroidism. Currently, information regarding long-term outcomes in cats treated with an oral fixed dose of radioiodine is limited and there are no practical markers to detect occult CKD in these cats. Objectives: This study aimed to describe the treatment outcomes following oral administration of a fixed dose (138 MBq; 3.7 mCi) of radioiodine in a sample of hyperthyroid cats and examine the correlation between serum TT4 concentrations before and after treatment. A second aim was to measure the serum SDMA concentration in hyperthyroid cats before and after treatment to determine the relationships between SDMA, creatinine and TT4 concentrations at both time points. Method: In a sample of cats previously treated with a fixed dose of oral radioiodine, TT4 concentration and renal clinical pathological parameters were documented before and after radioiodine treatment. Logistic regression was used to assess the relationship between TT4 concentrations before and after treatment. The differences in pre- and post-treatment variables for cats that had TT4 concentrations below or within the reference interval were also assessed. Renal parameters including urine specific gravity and serum SDMA, urea and creatinine concentrations were measured before and three months after receiving a fixed dose of oral radioiodine treatment in prospectively enrolled hyperthyroid cats. The Pearson correlation coefficient was used to determine the association between treatment and serum TT4, SDMA and creatinine concentrations. To assess agreement between serum SDMA and serum creatinine regarding categorisation of CKD staging, Goodman and Kruskal’s gamma statistic was used. Results: Of 162 cats, 133 (82%) had TT4 concentrations within the reference interval after treatment. Four (3%) and 25 (15%) cats had TT4 concentrations above and below the reference interval after treatment, respectively. The severity of hyperthyroidism at diagnosis, as measured by the percentage elevation of TT4 concentration above the reference interval, had no impact on the odds of cats having TT4 concentrations below the reference interval after treatment (OR = 1.00; 95% CI 0.96–1.05; p = 0.93). Over the follow-up period after radioiodine treatment, serum SDMA increased in 51 of 74 (69%) cats, whereas serum creatinine increased in 78 of 80 (98%) cats. A moderate correlation between serum SDMA and creatinine was seen after treatment (r = 0.523, p < 0.001) but not before treatment (r = 0.523, p = 0.23). Where assessable after treatment, serum SDMA and creatinine did not agree in the staging of cats with kidney dysfunction based on the International Renal Interest Society CKD guidelines. No significant correlation was seen between serum SDMA and TT4 concentration at any time point. Conclusions and relevance: When using an orally administered fixed dose of radioiodine for the treatment of feline hyperthyroidism, TT4 concentrations at diagnosis cannot be used to predict TT4 concentrations after treatment. The proportion of cats with TT4 concentrations below the reference interval after treatment was 15%. Further work is required to optimise oral radioiodine dosing to maximise euthyroidism. Extra-renal factors associated with hyperthyroidism appear to hinder the ability of SDMA to identify cats with occult CKD before treatment. Further work is required to elucidate the mechanism and impact on the performance of SDMA as a diagnostic test of renal function in hyperthyroid cats.