There were 3.6 times as many noncatastrophic fractures as catastrophic fractures in Thoroughbreds racing in Hong Kong between 2004 and 2011. Noncatastrophic fractures interfere with race training schedules and may predispose to catastrophic fracture. Future analytical studies on noncatastrophic racing fractures should be a priority for the racing industry.

The current clinical techniques for neuraxial needle placement in dogs are predominantly blind without prior knowledge of the depth required to reach the desired space. This study investigated the correlation and defined the relationship between easily obtainable external landmark variables in the dog; occipital–coccygeal length (OCL) and ilium wings distance (IWD), with the skin to epidural and intrathecal space distances using computed tomography (CT). The CT images of 86 dogs of different breeds were examined in this retrospective observational study. Images of dogs in sternal recumbency were optimized to the sagittal view. The distances between the skin and lumbosacral epidural space (LSE) and skin to sacrococcygeal space (SCE) were measured to the ligamentum flavum surrogate (LFS) line. The distance between the skin and the intrathecal space (ITS) was measured from the skin to the vertebral canal at the interlumbar (L5–L6) space. Measurements of the IWD and OCL were performed on dorsal and scout views, respectively. Linear regression equations and Pearson’s correlation coefficients were calculated between variables. Data were reported as mean (standard deviation). Significance was set as alpha < 0.05. After exclusion of four dogs, 82 CT scans were included. The depths were LSE 45 (15) mm, SCE 23 (10) mm, and ITS 50 (15) mm. There was a moderate correlation between OCL with LSE (=14.2 + OCL * 0.05 (r = 0.59, p < 0.0001)), and a strong correlation with ITS (=11.4 + OCL * 0.07 (r = 0.76, p < 0.0001)), while a very weak correlation was found with SCE (=14.0 + OCL * 0.02 (r = 0.27, p < 0.0584)). Similarly, with IWD, there was a moderate correlation with LSE (=10.8 + IWD * 0.56 (r = 0.61, p < 0.0001)), and strong correlation with ITS (=9.2 + IWD * 0.67 (r = 0.75, p < 0.0001)), while a weak correlation was found with SCE (=11.2 + IWD * 0.2 (r = 0.32, p < 0.0033)). Mathematical formulae derived from the multiple regression showed that the body condition score (BCS) improved the relationship between IWD and OCL and the LSE, SCE and ITS, while the addition of body weight was associated with multicollinearity. Further studies are required to determine the accuracy of the algorithms to demonstrate their ability for prediction in a clinical setting.

The study aimed to compare bupivacaine onset time when administered via epidural anaesthesia injecting both at the lumbosacral and sacrococcygeal spaces, spinal anaesthesia, and DPE in clinical dogs. A total of 41 dogs requiring neuraxial anaesthesia as part of their anaesthetic protocol were recruited. They were randomly allocated to receive an epidural injection in the sacrococcygeal space aided by the nerve stimulator (SCO), an epidural injection in the lumbosacral (LS), a subarachnoid injection (SPI), or a DPE. The onset of anaesthesia was assessed every 30 s after the injection by testing the presence of patellar ligament reflex. The number of attempts and time to perform the technique were also recorded. Data were analysed using a one-way ANOVA for trimmed means with post hoc Lincoln test and a Kaplan–Meier curve. The significance level was set at p < 0.05, and the results are presented in absolute values and median (range). There was no difference in the number of attempts required to complete the techniques between groups (p = 0.97). Epidural injections (LS and SCO) tended to be shorter than SPI and DPE techniques, but there was no statistically significant difference (p = 0.071). The time to the disappearance of patellar ligament reflex (Westphal’s sign) in the SCO group was longer than in any other group. In conclusion, all techniques provided a rapid block of the patellar reflex. The SCO technique was the slowest in onset, while the other groups (SPI, DPE, and LS) were faster and almost indistinguishable.

Resorption within cortices of long bones removes excess mass and damaged tissue, and increases during periods of reduced mechanical loading. Returning to high-intensity exercise may place bones at risk of failure due to increased porosity caused by bone resorption. We used microradiographic images of bone slices from highly-loaded (metacarpal, tibia, humerus) and minimally-loaded (rib) bones from 12 racehorses, 6 in active high-intensity exercise and 6 in a period of rest following intense exercise, and measured intracortical canal cross-sectional area (Ca.Ar) and number (N.Ca) to infer remodelling activity across sites and exercise groups. Large canals representing resorption spaces (Ca.Ar > 0.04 mm2) were 5- to 18-fold greater in number and area in the third metacarpal bone from rested than exercised animals (p = 0.005–0.008), but were similar in number and area in ribs from rested and exercised animals (p = 0.575–0.688). A weaker, intermediate relationship was present in tibia and humerus, and when resorption spaces and partially-infilled canals (Ca.Ar > 0.002 mm2) were considered together. The mechanostat may override targeted remodelling during periods of high mechanical load by enhancing bone formation, reducing resorption and suppressing turnover, but both systems may work synergistically in rest periods to remove excess and damaged tissue.

Fractures in Thoroughbred racehorses are an omnipresent welfare issue. Previous studies have often failed to adequately address the issue of fractures in racing and training because of the limitations associated with record keeping. Racehorses being rested from intensive exercise are also at greater risk of fracture on re-introduction to high intensity work. This thesis aims to accurately report first event fractures and determine racing and training fracture incidence rates in the highly controlled Thoroughbred racehorse population at the Hong Kong Jockey Club (HKJC) and to identify differences in bone remodelling (as defined in this thesis) between racehorses, which have been rested compared to horses in current high intensity exercise. Hong Kong to date of fracture, retirement, or end of the study period, whichever was first. Incidence rates for racing were expressed as catastrophic or non-catastrophic fracture events per 1000 race starts (Chapter Three). Training incidence rates were expressed as catastrophic or non-catastrophic fracture events per 10,000 horse days at risk (Chapter Four). The incidence rate for catastrophic fractures during racing was 0.6 per 1000 race starts (95% CI 0.4 -0.8) and for non-catastrophic fractures it was 2.2 per 1000 race starts (95% CI 1.8 -2.6). The incidence rate for catastrophic fractures in training was 0.08 per 10,000 horse days at risk (95% CI 0.05 -0.11), and for non-catastrophic fractures was 0.85 per 10,000 horse days at risk (95% CI 0.75 -0.96). The incidence rate of catastrophic racing fractures at the HKJC were lower when compared to the results of studies conducted in the UnitedStates (Estberg, Stover et al. 1996b) and higher than in the United Kingdom (Parkin, Clegg et al. In another study, bones were obtained post-mortem from horses in Exercised (n = 6) and Rested (n = 6) Groups who died for reasons unrelated to fracture or the fracture study. Exercised horses had been euthanized within seven days of high intensity exercise while Rested horses had been retired for one to four months and whose work level was much reduced before retirement. Six bone blocks were cut from each horse at the following locations; right third metacarpal bone (MCIII) where samples were collected from the mid-diaphysis, distal lateral metaphysis and medial condyle; right third metatarsal bone (MTIII) where a sample was collected from the lateral condyle; distal left tibia, and middiaphysis of the left tenth rib. Each bone block was cut to 250 µm thick specimens using a diamond 3 annular saw. Microradiographs were obtained using point projection digital microradiography (Faxitron) and analysed to identify radiolucent spaces indicative of recently formed resorption canals as a proxy for active bone remodelling. This study identified that resorption canals of all sections from MCIII and the tibia were significantly greater in the Rested Group compared with the Exercised Group (P < 0.05). There was no significant difference in the resorption canal density of the rib between the two g...