Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
12 results
Search Results
Item Comparison of gastrointestinal transit times in stabled Thoroughbred horses fed freshly cut pasture and three conserved forage-based diets(CSIRO Publishing, 2022-07) Fernandes KA; Rogers CW; Gee EK; Fitch G; Bolwell CF; Kittelmann S; Bermingham EN; Thomas DGContext: The type of forage offered to horses varies in physical form, moisture content and nutrient quality, and these variables could affect the intake, passage rate and digestibility of the forage consumed. Aims: To investigate the changes in passage rate of digesta through the gastrointestinal tract in horses fed four different forage-based diets (diet effect). Methods: Thoroughbred mares (n = 6) were stabled in loose boxes for 6 weeks. During Weeks 1, 3 and 5 (washout periods), all horses were fed freshly cut pasture, either in restricted quantities (Week 1) or ad libitum (Weeks 3 and 5). Using a 3 × 3 Latin square design during Weeks 2, 4 and 6, each pair of horses was abruptly transitioned to one of three conserved forage-based diets (chopped ensiled forage fed exclusively or with oats, or perennial ryegrass hay with oats) fed ad libitum. At the beginning of each week, indigestible polyethylene markers (n = 200) were administered to the horses via a nasogastric tube, followed immediately by transition to the new diet. Key results: There was a significant diet effect on the daily dry-matter intake of feed (P < 0.0001), percentage of time spent eating (P < 0.001), frequency of voiding faeces (P < 0.05) and quantity of faeces voided (P < 0.0001). There was a significant horse effect on the daily dry-matter intake of feed (P < 0.0001) and quantity of faeces voided (P < 0.0001), but no differences in the percentage of time spent eating or the frequency of voiding faeces. There were significant diet and horse effects on the time to recovery of the first marker in the faeces (P < 0.01 and P < 0.01 respectively) and the mean retention time of markers in the gastrointestinal tract (P < 0.05 and P < 0.001 respectively). Mean retention time was negatively correlated with feed intake and quantity of faeces voided (r2 =-0.51 and r2 =-0.64 respectively). Conclusions: Longer mean retention time was associated with a greater fibre content in the diet and a restricted feed supply, thus supporting the hypothesis that horses alter mean retention time on the basis of a nutrient absorption optimisation model. Implications: Feed composition, but also the quantities offered, may alter measurement of apparent feed digestibility in horses.Item The effect of early exercise on the articular cartilage and subchondral bone of the distal third metacarpal/metatarsal bones 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(Massey University, 2003) Dykgraaf, SusanneThe effect of early moderate exercise on articular cartilage and subchondral bone were investigated by comparing two groups of age and sex matched, pasture reared, 18 month old (± one month) Thoroughbred horses. The treatment group (n=6, 3 colts, 3 fillies) were exercised five days per week from 10 days of age on a purpose-built grass racetrack. The control group were managed identically but did not participate in an exercise programme. Articular cartilage samples were taken from all horses, from the palmar and dorsal regions of the left and right distal third metacarpal bones (Mc3) and the palmar region of the left third metatarsal bone (Mt3). The sites were selected from regions that sustain high (palmar region) and low (dorsal region) load during exercise. The fresh articular cartilage samples were incubated with fluorescent stains (calcein-AM and propidium iodide) and examined under confocal laser scanning microscopy to assess chondrocyte viability. The number of viable and dead chondrocytes at each site was determined based on the fluorescent staining characteristics The subchondral epiphyseal bone mineral density adjacent to the articular cartilage sample sites was measured using computed tomography data from regions of interest which were 2mm proximal to the interface of calcified cartilage and subchondral bone. There was a 14% greater percentage of viable chondrocytes in the exercised horses (p=0.00l), and a 34% greater percentage of viable chondrocytes at the control palmar regions compared to control dorsal regions (p=0.001). One exercised horse and five control horses had subtle macroscopic features consistent with osteoarthritis (OA) in the metacarpo(tarso)-phalangeal joints. Variation in chondrocyte viability was less in palmar and dorsal sites from exercised animals, and palmar sites from control animals. An association between percentage of dead chondrocytes and sclerosis of the subchondral bone (SCB) could not be identified. Lower chondrocyte viability occurred independently of SCB sclerosis. The sequence of initiating events leading to reduced articular cartilage viability appeared to be unassociated with SCB sclerosis at the sites of distal Mc3/Mt3 under the moderate exercise regimen imposed. The effect of early exercise on the articular cartilage and SCB of young Thoroughbred horses has been further elucidated. Early exercise appeared to have beneficial effect on the viability of the articular cartilage sampled in this group of horses. The abnormalities detected may have been the earliest stages of idiopathic OA, but the relative and temporal involvements of articular cartilage and SCB remain undefined.Item 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(Massey University, 2004) Moffat, TrishThe 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.Item Investigation into the influence of yearling sale production parameters on the future career longevity and success of New Zealand thoroughbred race horses : a thesis presented in partial fulfillment of the requirements for the degree of Masters of Science in Agricultural Science (equine) at Massey University, Palmerston North, New Zealand(Massey University, 2011) Waldron, Kristi LouiseFew studies have investigated the influence of yearling sale production parameters on racing performance of Thoroughbred horses. The aim of this study was to quantify the impact of yearling sales parameters, in particular dam (mare) age at the time of conception, on future career success and longevity in a population of Thoroughbred racehorses in New Zealand. A retrospective cohort study was used to investigate racing success and longevity in a population of Thoroughbred horses in New Zealand, over eight and a half racing seasons. Retrospective records of the 2002 born Thoroughbred foals in New Zealand were obtained from the New Zealand Bloodstock (NZB) online database and the New Zealand Thoroughbred Racing (NZTR) database. Logistic regression models using the binary outcomes trial, race and prize money earned were analysed with exposure variables. Cox regression survival analysis was used to investigate the association between the number of race starts and the time to cessation of racing. Linear regression was preformed to assess the effect of exposure variables with the outcome measure prize money earned (ln, $NZ). A total of 513 horses ran in 8,261 flat races, in New Zealand, during the study period. Of all the horses that had at least one race start (n=513), the median number of race starts per horse was twelve (IQR 5-22). The age of a horse’s dam (mare) at the time of conception was not significantly associated with; 1) her progeny obtaining a trial or race start, 2) her progeny racing and earning >$1 prize money, 3) the amount of prize money earned by her progeny, and 4) longevity of her progeny’s career. Female horses had less race starts during their career (P=0.019) compared to male horses. The median number of race starts for a female was eleven (95% C.I 9-14) whereas, the median number of race starts for a male was thirteen (95% C.I. 10-15). Horses catalogued in the select session were more likely to earn prize money (P=0.029) ii compared to horses catalogued in the premier session. Horses catalogued in the festival session were more likely to cease racing compared to horses catalogued in the premier session (P=0.018). The median number of race starts for a horse catalogued in the premier session was ten (95% C.I. 8-14) compared to fourteen (95% C.I. 12-16) for the select session and ten (95% C.I. 8-13) for the festival session. Horses that had started in a trial were more likely to start in a race (P<0.001) and earn prize money (P<0.001) compared to horses that had not started in a trial. As the number of years racing increased the likelihood of a horse ceasing racing decreased (p<0.001). Linear regression showed that total career starts was the greatest predictor in determining the amount of prize money a horse will earn. Horses that had more than twenty-five race starts were more likely to earn more prize money (ln) compared to horses that had less than twenty-five race starts (P<0.001). The results of this study highlight associations, or lack thereof, between yearling sales parameters and outcome measures of performance and may influence the future buyer behaviour in the New Zealand Thoroughbred market.Item Reproductive performance and the transition period of thoroughbred mares in New Zealand : evidence and implications for future alternative management strategies : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand(Massey University, 2012) Hanlon, David WilliamThe aims of this research were to investigate the reproductive performance of Thoroughbred mares in New Zealand, to examine the use of intravaginal progesterone to manage transitional mares and to develop a potential model for haemorrhagic anovulatory follicle (HAF) development in the mare. Firstly, a prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during three consecutive breeding seasons (2006-2008). A total of 1482 individual mares contributed 2007 mare years and 3402 oestrous cycles over the three breeding seasons. The mean first-cycle pregnancy rate was 53.6%, the end-of-season pregnancy rate was 85.3% and the foaling rate was 80.2%. The length of the breeding season was relatively short with 87% of services occurring in the 91 day period between 1st September and 30th November. Multivariable analyses revealed that reproductive performance was influenced by two main mare-related factors; the age of the mare and her reproductive status (dry or foaling). Increasing mare age significantly reduced the first-cycle pregnancy rate, reduced the end-of-season pregnancy rate and increased the interval from the start of the breeding season to conception. In terms of reproductive status, dry mares had a significantly higher first-cycle pregnancy rate and end-of-season pregnancy rate compared with foaling mares. The majority of variation in reproductive performance was associated with mare-level factors and the contribution of the stallion and stud farm was relatively minor. Transitional mares treated with intravaginal progesterone at the start of the breeding season were served two weeks earlier than untreated control mares. In the first 21 days of the season, 95% of treated mares were served compared with 43% of control mares. Treated mares also conceived earlier and had a higher end-of-season pregnancy rate than control mares. Follicle development in response to intravaginal progesterone treatment iii appeared to be mediated through a close temporal association between progesterone, FSH and LH during treatment. In the last study, transplantation of chorionic girdle into non-pregnant mares resulted in elevated eCG concentrations in all mares and the development of multiple HAFs in the treated mares over a prolonged time-span. In conclusion, this research has, i) identified the most important factors associated with the reproductive performance of New Zealand Thoroughbred mares, ii) determined that intravaginal progesterone treatment is a suitable management tool for transitional mares and iii) created a model for HAF development in the mare.Item The association of 2-year-old training milestones with racing performance in standardbred and thoroughbred horses in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree Master of Science in Animal Science, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2011) Tanner, Jasmine ClaireThis thesis includes epidemiological studies conducted to measure the association between the attainment of training milestones by Standardbred and Thoroughbred horses at two years of age and subsequent racing performance. Additionally, the quantification of racing performance is comprehensively reviewed to identify robust parameters to measure racing success. Retrospective records of all Standardbred and Thoroughbred horses born in the 2001/2002 season were obtained and analysed separately. The three training milestones used were: registered with a trainer, trialled and raced. Racing performance outcomes were: length of career, in number of years raced and number of race starts, and total earnings. Horses that were registered with a trainer, trialled, or raced as two-year-olds had more race starts and more years racing than those horses that achieved the milestones at a later age. Additionally, horses that achieved the training milestones as two-year-olds were more likely to win or be placed (first-to-third) in a race, and earned more money than horses that achieved the milestones at a later age. Approximately one-third of the horses born in both the Standardbred and Thoroughbred foal crop failed to achieve the first training milestone indicating high levels of wastage. The results of this thesis suggest that there is a strong association between the attainment of training milestones at two years old with positive career outcomes.Item Bone mineral density characteristics of the third metacarpal /metatarsal distal epiphysis of thoroughbred horses : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Manawatu, New Zealand(Massey University, 2012) Bogers, Sophie HelenThis thesis includes two studies using non-invasive imaging techniques to quantify, in detail, the bone mineral density (BMD) characteristics of the distal third metacarpal (Mc3) and metatarsal (Mt3) epiphyses of Thoroughbred horses associated with exercise exposure and condylar fracture. Additionally, the relationship between the bone structure of the distal Mc3/Mt3 epiphysis and incurred cyclic loading, as well as techniques for imaging the area non-invasively, are reviewed. Mt3 bones from fourteen trained or untrained Thoroughbred horses and Mc3 bones from fourteen Thoroughbred racehorses with or without condylar fracture were scanned using peripheral quantitative computed tomography (pQCT) at a site on the distal epiphysis. The relative proportions of volumetric bone mineral density (BMDV) and the spatial distribution of BMDV were quantitatively assessed using conventional and ArcGIS software. The relative proportion of voxels within nine threshold categories of BMDV and spatial statistics of BMDV distribution were compared for regions of interest in the palmar/plantar epiphysis between respective treatment groups; trained vs. untrained controls or fractured vs. non-fractured controls. In study one, trained horses had a significantly higher (P=0.006) proportion of high BMDV voxels and a significantly lower (P=0.006) relative proportion of low BMDV voxels than controls in the central condylar regions of the plantar Mt3 epiphysis. In other regions of the plantar epiphysis the trained horses also had a significantly higher (P=0.006) relative proportion of high BMDV voxels than controls; however, there were no significant differences for the relative proportion of low BMDV voxels. These relationships were also evident with multiple correspondence analysis. There was strong to marked clustering of high BMDV voxels in the central condylar region of all of the trained horses (I = 0.64 - 1.0, P = 0.01) and no clustering of low BMDV voxels. In contrast, half of the control horses had clustering of high BMDV voxels, which was weak to strong (I = 0.64 - 1.0, P = 0.01) and there was weak to moderate clustering of low BMDV voxels in the lateral and medial central condylar regions (I = 0.45-0.62, P = 0.01 and I = 0.45-0.57, P = 0.01, respectively). In study two, there were no significant differences between the median age (P = 0.7), number of race starts (P = 0.5), the relative proportion of BMDV voxels, or the spatial distribution of BMDV voxels in regions of the palmar Mc3 epiphysis between the fractured and control groups. The results of this thesis suggest that the response of bone to exercise is specific in relation to anatomical site, the thresholds of BMD that change, and the spatial distribution of BMD. In both studies the exercise exposure was responsible for much of the variation in the relative proportions and the spatial distributions of BMDV. The clinical relevance of these findings are that detailed quantification of previous exercise exposure needs to be considered when determining if a BMD response of the Mt3/Mc3 epiphysis is part of a physiological or pathological finding.Item A study of some muscles of the equine larynx and soft palate : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Surgery(Massey University, 1984) Anderson, Laurence JohnThe purpose of this study was to determine the age of onset, incidence and severity of neurogenic disease in the intrinsic laryngeal muscles of a single breed of competitive horse, the New Zealand Thoroughbred. Some palatal muscles from these horses were also studied to ascertain whether neurogenic disease occurred in them. The left and right dorsal cricoarytenoid, lateral cricoarytenoid, transverse arytenoid, ventricular, vocal, cricothyroid, hyoepiglottic, palatopharyngeal, palatine levator, palatine, and palatine tensor muscles were collected from some or all of 53 Thoroughbred horses. Forty-six of the horses had no history of upper respiratory tract abnormalities, six had suffered from idiopathic laryngeal hemiplegia and one from laryngo-palatal dislocation. For comparative purposes similar muscles from three ponies were also studied. The muscles were weighed and then frozen sections were prepared from them. Some of these were stained with haematoxylin and eosin and others to demonstrate the activity of myosin adenosine triphosphatase, succinate dehydrogenase and glycogen phosphorylase. These sections were then studied to determine the muscle fibre types present and their proportions. The mean sizes of the groups of myosin adenosine triphosphatase low reacting fibres were measured as were the mean cross sectional areas of the fibres. Abnormal staining characteristics of the fibres were noted along with histological signs of denervation and reinnervation. Where possible this information was analysed to determine the significance of the differences observed between the measured mean values. A difference in weight between some of the left and right laryngeal muscles was found to be very common in Thoroughbred horses with no history of upper respiratory tract abnormalities. The left lateral cricoarytenoid muscle was lighter than the right in approximately half of these horses. This difference was significant between the muscles of these horses over three years of age and was most obvious in the muscles of the geldings. The left and right dorsal crico-arytenoid muscles showed similar but not such marked differences. These differences were more obvious in the laryngeal hemiplegic horses. The fibres of the intrinsic laryngeal muscles were predominantly highly reactive for the enzyme myosin adenosine triphosphatase with the ventricular and vocal muscles having the highest proportions of these fibres and the cricothyroid and hyoepiglottic muscles the lowest. Glycogen phosphorylase reactivity in these muscles was again predominantly high, and the fibres were almost exclusively, highly reactive for succinate dehydrogenase. Neurogenic disease appeared to have an influence on the proportions of fibre types present in affected muscles. The incidence of larger groups of myosin adenosine triphosphatase low reacting fibres in some of the left than right intrinsic laryngeal muscles was also very common in Thoroughbred horses with no history of upper respiratory tract abnormalities. Eighty percent of these horses over three years of age had larger groups in their left than right lateral cricoarytenoid muscles and the youngest horse where this difference was noted was six weeks Old. The adductor muscles showed more evidence of this side difference in group size than the abductor muscles. The mean cross sectional area of the fibres of the intrinsic laryngeal muscles studied increased till approximately the end of the third year of a horse's life. Neurogenic disease eventually reduced the cross sectional area of the fibres of affected muscles but early in its course it may have produced an increase in the mean cross sectional area of fibres. This increase occurred in mildly affected and also in some unaffected muscles. The latter may have been required to increase their activity to compensate for inefficient function in atrophied muscles. The histological signs of denervation and reinnervation were also very common in the intrinsic laryngeal muscles supplied by the left recurrent laryngeal nerve. These signs were noted in almost 70% of the left lateral cricoarytenoid muscles from horses over one year of age, with no history of upper respiratory tract abnormalities. The incidence of these signs in the dorsal cricoarytenoid muscle was lower but they appeared suddenly and severely in the left muscles of horses during adolescence and early adult life. In the cricothyroid muscle which is not supplied by the recurrent laryngeal nerve, the only histological signs of this nature appeared in the muscles of a few of the aged horses. In the palatal muscles examined there was no evidence of a difference in weight between the left and right muscles and most of their fibres were highly reactive for the three enzymes studied. There was no evidence of fibre type grouping resulting from denervation and reinnervation and none of the other histological signs resulting from severe neurogenic disease were noted.Item Epidemiological studies of early exercise and measures of training and racing performance in thoroughbred racehorses : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology, Massey University, Palmerston North, New Zealand(Massey University, 2011) Bolwell, Charlotte FrancesThis thesis includes a series of epidemiological studies conducted to quantify the exercise regimens of Thoroughbred yearlings during their sales preparation and 2- and 3-year-old race training. Additionally, this thesis aims to establish if there are associations between the exercise regimens and training and racing performance at two years of age. Cross-sectional and cohort studies quantified the components of the exercise regimens used during sales preparation on stud farms in New Zealand. Exercise was a common practice during sales preparation. The type and amount of exercise was often tailored to individual horses. Overall, exercise varied by gender, the month of preparation, and between farms indicating that the exposure to exercise during sales preparation was not the same for all horses. Survival analysis identified different horse and exercise risk factors for voluntary, involuntary, and musculoskeletal interruptions during training. Specifically, there were strong associations between increased total hand walking time and reduced chance of voluntary interruptions, and more time walking on a mechanical walker increased the risk of involuntary interruptions. Other horse and training factors, such as trainer, gender, age at the start of training, and the distance accumulated at canter and high speed, were associated with the time to interruptions during training. Interruptions before the first trial were associated with an increased time to the first trial or race and a decreased chance of starting in a trial. Accumulating shorter distances and fewer events at high speed were both associated with a decreased chance of a trial or race start. Longer distances accumulated at high speed were associated with a decreased time to the first trial. No associations were found between the exercise accumulated during sales preparation and the time to the first trial during training. Overall, the exercise accumulated during sales preparation was associated with a measure of training performance, whilst the timing of interruptions and the accumulation of exercise during training have implications for reaching important training and racing milestones. The results of this thesis indicate that current exercise regimens could be modified to enhance the training and racing performance of Thoroughbred racehorses.Item The effect of exercise on the collagen fibril morphology of the digital flexor tendons of the thoroughbred : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1996) Patterson-Kane, Janet Claire; Patterson-Kane, Janet ClaireA series of studies was conducted to test the hypothesis that galloping exercise changes the morphology of collagen fibrils in the superficial digital flexor tendon of the equine forelimb. Tendons were examined from three groups of horses, namely wild horses, randomly sourced thoroughbred horses submitted for necropsy, and thoroughbreds from an experimental exercise trial. All tendons examined were from horses with no history of superficial digital flexor tendonitis, and all were macroscopically normal. Three studies involved the measurement of collagen fibril bundle 'crimp' morphology. The crimp, a planar waveform followed by the fibrils, is believed to determine in part the mechanical behaviour of tendon. The first study involved measurement of crimp angle and period length in central and peripheral regions of tendons from wild ponies ranging in age from two to over ten years, which had obviously never undergone training. Horses of ten years of age or older showed a mean crimp angle in the central region which was lower than that in the periphery. It was concluded that the reduction in central region crimp angle with age in untrained horses is a normal fatigue effect. The second study involved measurement of crimp parameters in central and peripheral regions of tendons from horses of two years and over which had been submitted for necropsy to Massey University. These horses were separated into 'exercised' and 'non-exercised' groups based on whether their most recent function had involved competitive galloping exercise. Five of the eight exercised horses under ten years of age had a lower mean crimp angle and length in the central region than in the peripheral region. No un-exercised horses in this age group showed lower values for either parameter in the central region as opposed to the periphery. It was therefore concluded that rapid high-strain cycling of the tendon occurring during galloping exercise modifies normal age-related changes in the crimp morphology of the superficial digital flexor tendon core. For the third study, crimp angle and length were measured in tendons from five thoroughbreds (39±1 months of age) which had undergone a specific 18 month exercise regime involving galloping on a high-speed equine treadmill, and from six age- and sex-matched thoroughbreds which had undergone walking exercise only during that period. Central region crimp angle and length were significantly lower in the tendons of exercised horses compared to the controls. Four of the five exercised horses showed a significantly lower crimp angle in the central region than in the periphery, and three of these horses also showed a lower central crimp length. The peripheral angle was significantly greater in the exercised horses than in the controls. This was evidence that a specific and defined regime of high-strain cycling of the superficial digital flexor tendon modified age-related crimp morphology changes in the central region. Two studies were undertaken to investigate the effect of the above defined exercise regime on collagen fibril diameter distributions in the superficial digital flexor tendons, and in the deep digital flexor tendons and suspensory ligaments from the same horses. Central region fibrils in superficial digital flexor tendons from exercised horses had a significantly lower mass-average diameter than those from the control horses, whereas peripheral region fibrils from the two groups did not differ significantly. In the second study collagen fibril mass-average diameters in both regions of the deep digital flexor tendon and the suspensory ligament were not found to differ significantly in exercised horses compared to controls. It was concluded that the exercise regime had caused breakdown of large diameter collagen fibrils in the core of the superficial digital flexor tendon. The fact that such a change did not occur in the suspensory ligament was suggested to be due to a difference in distribution of load between the suspensory ligament and superficial digital flexor tendon during galloping, or due to differences in distribution of such changes along the lengths of the two structures. The final study involved an age-related analysis of crimp parameters, collagen fibril diameters and biochemical factors in thoroughbreds from foetuses to 3 years of age. It was suggested on the basis of the limited results, that collagen fibrils in the central region of the superficial digital flexor tendon become mature between one and two years of age. It is proposed that the observed reductions in crimp morphology and collagen fibril mass-average diameter in the core of the superficial digital flexor tendon in response to galloping exercise represent microtrauma, as they would lead to weakness of the structure and predispose it to overloading and further damage. The mechanisms involved are suggested to involve slippage and/or separation of subfibrils, and a mechanism for the development of tendon core lesions is hypothesized. The use of the present information for the prevention of tendonitis is discussed.