Veterinary Science - Theses
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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.
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ItemAngiotensin-converting enzyme (ACE) in horses and its relationship to performance and fitness( 2010)This body of work concerns studies investigating aspects of ACE activity in the horse. Since very little information is available in the existing literature regarding this topic, basic research included assay validation, comparison of methods, and sample stability testing. Further investigations included the influence of environmental factors on circulating ACE activity, including diurnal and seasonal variations and the effects of training and acute exercise. This research sought to investigate whether there was an association between ACE phenotype and performance for different equestrian modalities, namely flat racing and endurance. Subsequently, aspects of the ACE genotype, ACE activity in tissues and whether there was an association between ACE activity and diseases of metabolic or pulmonary origins were investigated. Assay testing demonstrated that different methods are not comparable, therefore caution is required when interpreting data obtained with different protocols for ACE measurement. Also, sample stability testing provided evidence that equine ACE is more labile than its human counterpart, requiring strict handling and storage to achieve repeatable and consistent results. Data demonstrated that equine ACE has a seasonal variation, peaking during spring of the Southern Hemisphere, whereas no significant circadian rhythm of the enzyme was observed. Results demonstrate that greater ACE activity is associated with improved performance indices in maiden Thoroughbreds, and is also associated with distance successfully raced by Thoroughbred racehorses, both under flat racing conditions. ACE activity in equine plasma is responsive to both acute and chronic exercise, with increased levels proportional to workload. This has important implications with regard to selection of horses suitable for particular types of event, and also in the assessment of fitness. In relation to clinical conditions, although ACE activity was not associated with the systemic response to an experimental endotoxic challenge, horses admitted to a referral centre with colic had improved likelihood of being discharged if their ACE activity in plasma was higher at admission. ACE activity was not a good indicator of pulmonary disease diagnosed via endoscopy only, but there is an indication that ACE activity might be correlated to severity of chronic lung disease. ACE activity in equine lungs is higher than in the kidneys and the heart, and data suggests that acute lung injury may cause a reduction in both plasma and lung tissue ACE activity, whereas chronic pulmonary disease leads to an elevation in plasma ACE with reduced lung tissue ACE activity. ACE genotyping demonstrated that horses carrying a single copy of the H6 haplotype had lower levels of circulating ACE activity, but since only 9.5% of animals in the sample had the H6, the association was poor. ACE activity in equine plasma was demonstrated to be a better tool for assessing suitability for athletic events or training than ACE genotype, and to have potential as an accessory tool to monitor performance and as an indicator of disease course in some clinical situations.