Summary Reasons for performing study: Overstrain injuries to the superficial digital flexor tendon (SDFT) and suspensory ligament (SL) are among the most common musculoskeletal injuries which contribute to the considerable wastage of racing Thoroughbreds. Many epidemiological studies have demonstrated the prevalence of and risk factors for tendon injury when racing but have not included those injuries sustained during training. However, since tendon injury during training is seen commonly in clinical practice, it is appropriate to determine the overall prevalence of tendon injury sustained during both training and racing. Objective: To determine the prevalence of overstrain injury to the SDFT and SL during training and racing among Thoroughbred flat racehorses in Japan in 1999. Methods: A retrospective study was performed using a sample population of 10,262 Thoroughbred racehorses. The medical information database of Thoroughbred racehorses registered by the Japan Racing Association (JRA) in 1999 was analysed for SDFT and SL overstrain injury diagnosed by a veterinarian employed by JRA during training and racing. Jump racehorses were excluded from this study. Results: The prevalence of forelimb SDFT tendonitis and SL desmitis was 11.1% (1130 cases) and 3.61% (370 cases) of the population, respectively. In the hindlimb, there were 0.06% (6 cases) and 0.14% (14 cases), respectively. Risks of SDF tendonitis in the forelimb in 3‐year‐olds or older horses were significantly higher than in 2‐year‐olds. In contrast, the risk of SL desmitis in the forelimb at age 3 and 4 years was 2.23 and 2.11 times higher, respectively, than in 2‐year‐olds, but this increased to 5.07 times in those age ≥5 years. Entire males were at greater risk in comparison to females and geldings. Conclusions: The results suggest that the prevalence of SDF tendonitis and SL desmitis in the forelimb was associated with the horse's age and sex. The prevalence of SL desmitis increased further with age compared with SDF tendonitis, possibly reflecting a more rapid accumulation of degeneration in this structure. Potential relevance: The age‐related risk demonstrated in this study provides further support that overstrain injuries are associated with accumulated degeneration. These data provide a valuable resource for further research into the aetiology of tendon injury in the racehorse.

Sternal marrow aspiration as described is a safe and reliable technique to obtain MSCs for orthopaedic cell-based therapies.

ABSTRACT. Six live horses with various stages of acute to chronic superficial digital flexor (SDF) tendinitis were examined using magnetic resonance imaging (MRI). In each case, MRI findings were compared to the corresponding ultrasonographic (USD) and histologic findings, to establish the usefulness of MRI. In the acute cases, lesions characterized by hemorrhage were well defined as high sig nal intensity on MRI and hypoechoic regions on USD. Chronic tendon fibrosis was slightly hyperechoic and difficult to distinguish from the normal tendon tissue around the original injury by using USD. In contrast, MRI visualized the chronic lesion as a low intensity signal, which could be distinguished from the black background of the normal SDF tendon tissue. This study clearly demonstrated MRI was the better imaging modality for the objective detection of chronic scar tissue in live horses. These findings, from living horses, suggest an advantage of MRI in the clinical application to diagnose tendinitis in cases where there is chronic scar tissue that is diffi cult to discern on USD. KEY WORDS: equine, MRI, tendinitis.

SummaryMost skeletal tissues are thought to adapt to the mechanical environment they experience. While this has been demonstrated for muscle and bone, previous studies in the mature horse have failed to demonstrate adaptation in the superficial digital flexor tendon (SDFT), which suffers a high frequency of injury. This study tested the hypothesis that imposed exercise during growth would result in an increase in SDFT cross-sectional area (CSA). Fourteen Thoroughbred foals were divided into 2 sex-matched groups. A control group received 4 h pasture exercise and an exercise group had the same amount of pasture exercise with an additional short period of treadmill exercise daily from age 2-15 months. Activity at pasture was assessed objectively using a visual system. There was no significant difference in pasture activity between groups, although males were more active than females. The exercise programme resulted in a significantly larger tendon CSA in the exercise group at several, but not all, timepoints, which may be attributed to levels of variance. However, there was a significantly greater rate of increase in tendon CSA as a function of time in the exercised compared to the control group. This is the first evidence to suggest that tendon development can be modulated by exercise during growth in the horse, potentially increasing the ability of tendon to withstand the rigours of later athletic activity.

Results suggest that longer mean distance per race, heavier mean body weight at race time, steeplechase experience, and sex (male) increased the risk of SDFT injury in Thoroughbred racehorses.

Objective To identify morphologically the locations of equine corneal epithelial stem cells (CESCs) and to culture these cells. Animals studied We studied the eyes of 12 adult thoroughbred horses. Procedures Eye tissues were immunostained for two positive stem cell markers (p63, CK14) and one negative marker (CK3) to identify the locations of CESCs, so we could compare their immunostaining patterns with those of human stem cells previously reported. We compared the proliferation rates and morphological features of epithelial cells isolated from the corneal limbus and central cornea.Results Undifferentiated cells expressing the same immunostaining pattern as human CESCs were present in the equine corneal limbus. Cultured epithelial cells isolated from the limbus expressed the same immunostaining pattern that CESCs show histologically, but cells isolated from the central cornea did not proliferate and could not be evaluated. Conclusions Equine CESCs were localized in the epithelial basal layer of the corneal limbus, where melanocytes reside. They could be cultured without loss of their undifferentiated nature. When collecting such stem cells, it may be useful to harvest and culture corneal epithelial tissues in the limbus where melanocytes serve as an indicator of the collecting area.

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