The effect of early conditioning exercise on the cross sectional area of the superficial digital flexor tendon of young thoroughbred horses : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand

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The effect of conditioning exercise on the ultrasonographic cross sectional area (CSA) of the superficial digital flexor tendon (SDFT) of young Thoroughbred horses was investigated. Two groups of pasture-reared foals were matched for age and sex, and allocated into conditioned (n=18, 6 colts, 12 fillies) and control groups (n=15, 4 colts, 11 fillies). The conditioned group were exercised over 1030m on a purpose-built 515m oval grass track, for five days per week, from ten days of age until completion of the study (eighteen months of age). Conditioning exercise was in both a clockwise and counter-clockwise direction, with the initial velocity being 4.20 ms-1, which was increased to 5.56 ms-1 at five months of age, and to 6.66 ms-1 at eight months of age, with the addition of a 250m sprint at 12 ms-1. All foals underwent a thorough clinical examination and conformation assessment at four days of age. which was repeated monthly throughout the study period. The SDFT at the mid-metacarpal level of both left and right forelimbs were examined clinically and ultrasonographically in all animals at five, eight, twelve, fifteen and eighteen months of age. All ultrasonographic images were obtained using a Sonosite® 180 ultrasound machine with a linear 10-5 MHz transducer and a LA5 HRS acoustic stand-off. Captured images were exported to a Pentium computer and the CSA measured with Scion image, using the average of three measurements for statistical analysis. Twelve animals were euthanascd at eighteen months of age (6 conditioned, 6 control), and CSA measurement from digital images of transected SDFT at mid-metacarpal level were used to validate ultrasonographic CSA measurements. At no time during the course of the study were palpable tendon abnormalities detected in either conditioned or control groups, nor was there any ultrasonographic evidence of tendonitis in the SDFT at the mid-mctacarpal level in any of the animals. There was no statistically significant difference in mean CSA between conditioned and control animals at any age, nor between colts and fillies. No relationship between mean CSA, bodyweight or body condition score could be established. There was a good linear correlation between in-vivo ultrasonographic CSA obtained prior to post-mortem and in-vitro CSA obtained at post-mortem (R2 = 0.8881), with the in-vitro CSA being 10% larger. In this novel conditioning programme, early conditioning exercise did not induce a change in the ultrasonographic CSA of the SDFT of the conditioned group, when compared to that of the control animals. When measured ultrasonographically, the ability of the immature SDFT to undergo an adaptive response to conditioning exercise appears to be limited. With the sensitivity of current in-vivo measurement techniques, if there are any subtle changes in SDFT CSA in response to conditioning exercise, such changes are likely to remain undetected. Histological and biochemical assessment of harvested tissue was not performed for the purpose of this thesis (these are currently being analysed for another study) and may reveal changes in the SDFT induced by conditioning exercise, at a cellular or molecular level.
Flexor tendons, Thoroughbred horses, Tendonitis