Gait and speed as exercise components of risk factors associated with onset of fatigue injury of the third metacarpal bone in 2-year-old Thoroughbred racehorses.
OBJECTIVE
To determine the degree to which components of the training program of 2-year-old Thoroughbred racehorses influence their susceptibility to fatigue injury of the third metacarpal bone (bucked shins).


METHODS
226 two-year-old Thoroughbred racehorses.


METHODS
Daily training information and health reports on 2-year-old Thoroughbreds were compiled from records provided from 5 commercial stables. For each horse, data (exercise variables) were collected that comprised distance jogged (approx speed of 5 m/s), galloped (approx 11 m/s), and breezed (approx 15 to 16 m/s) until a single instance of bucked shins was reported. Data were coded for analysis using cross-tabulation, graphic, and survival techniques.


RESULTS
Of 226 horses, 56 had bucked shins, 9 completed the observation period without bucked shins, and 161 were lost to follow-up. Distinct training strategies were used at stables resulting in significantly different survival profiles among stables. Mean (+/- SD) allocation of exercise to breezing was 0.15 +/- 0.13 miles/wk (maximum, 0.64 miles/wk), to galloping was 4.47 +/- 1.52 miles/wk (maximum, 9.56 miles/wk), and to jogging was 2.34 +/- 1.70 miles/wk (maximum, 8.53 miles/wk). Survival (ie, lack of bucked shins during 1 year of monitoring) was found to be significantly reduced by exercise allocation to breezing, significantly increased by exercise allocation to galloping, and uninfluenced by exercise allocation to jogging. The log of the hazard ratio was reduced by 4.2 +/- 1.5/mile breezed and increased by 0.3 +/- 0.1/mile galloped.


CONCLUSIONS
Relationships between different gaits and speeds in the training regimen influence the incidence of bucked shins. To reduce the incidence of bucked shins, trainers should consider allocating more training effort to regular short-distance breezing and less to long-distance galloping.
Boston
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RC
Department of Clinical Studies, School of Veterinary Medicine, New Bolton Center, University of Pennsylvania, Kennett Square 19348, USA.
Nunamaker
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DM
D000818:Animals; D001847:Bone Diseases / Q000209:etiology / Q000517:prevention & control / Q000662:veterinary; D015331:Cohort Studies; D005221:Fatigue / Q000503:physiopathology / Q000662:veterinary; D005684:Gait / Q000502:physiology; D006734:Horse Diseases / Q000209:etiology* / Q000517:prevention & control; D006736:Horses / Q000293:injuries* / Q000502:physiology; D008663:Metacarpus / Q000293:injuries*; D010522:Periostitis / Q000209:etiology / Q000517:prevention & control / Q000662:veterinary*; D010805:Physical Conditioning, Animal / Q000009:adverse effects* / Q000706:statistics & numerical data; D011446:Prospective Studies; D012307:Risk Factors; D018709:Statistics, Nonparametric; D016019:Survival Analysis