Aust Vet J Vol 75, No 10, October 1997, pp 751-752
DL. Evans
Department of Animal Science
University of Sydney
NSW 2006JS. Walsh
RJ Walsh and Son Pty Ltd
122 Gow St
Padstow
NSW 2211Many factors contribute to the incidence of injury and lameness in Standardbred horses. These include conformation, nature of the training and racing programs, adequacy of diagnosis and treatment of limb abnormalities, and the condition and banking or gradient of the surface on which the horses are training and racing. Lameness may represent one of the greatest threats to the health and racing careers of Standardbred racehorses(1). Underbanked semicircular curves cause gait asymmetries in trotters exercising at high speeds, with horses leaning towards the centre of the curve and shifting their hindquarters outwards (2). This results in a difference in the width of the two diagonal forelimb to hindlimb distances, and is associated with abnormal fetlock movement. It was argued that this asymmetry of gait probably predisposed to lameness, because it is associated with differences in temperature of left and right limbs after exercise (2). Recommendations have been made concerning appropriate design of racetracks that would reduce the effects of centripetal force on the gait of Standardbred horses (3,4). Fredricson et al (1) argued that optimal track design is essential to enhance performance and to reduce the incidence of lameness, and that the design of tracks should be critically examined. High speed cinematography was used to study symmetry of gait in horses as they pace at racing speed around a turn, and considerable asymmetry was described, but it was concluded that the technique should not be used to judge standards of racetrack design (5).
The aim of this study was to test the hypothesis that an increase in the degree of banking of the turns results in decreased injury and lameness rates after racing in Standardbred horses.
In 1994 the NSW Harness Racing Club increased the banking at the Harold Park racetrack from 4.8 to 5.7 degrees. The change in banking was not accompanied by any change in track length or width. The effects of this reconstruction on the lameness and injury rates were assessed by retrospectively analysing records of injuries and numbers of starters in races.
Records from a 23 month period before the change to the track banking (February 1992 to December 1993) and for a 23 month period after the change (February 1994 to December 1995) were examined. The numbers of injuries and lameness incidents were obtained from the records of the attending veterinary surgeon. The injuries and lameness included those diagnosed by the veterinarian after a race, and those brought to the attention of the veterinarian by the trainer, owner, or stewards. The incidence of minor injuries and major, more serious injuries and/or lameness were recorded. Major injuries were defined as those that caused the veterinariamn to advise the stewards that the horse needed to be examined by a veterinary surgeon before it's next race. Most of the horses with major injuries were also barred from racing for at least 1 week as a result of the suspected or actual injury or lameness.
Injury rates for a 23 month period before and after the track reconstruction were calculated by dividing the number of injuries by the number of starters, and expressed as numbers of injuries per 1000 horse-races. Numbers of horses racing at each race meeting were obtained from the records of the NSW Harness Racing Authority. Injury rates before and after track redesign were compared by chi-square test.
There were 13,114 horse-races over the 23 month period before the change to the track banking, and 14,137 after the change. Figure 1 illustrates the rates of total injuries and lameness events in each month over the 23 month period before and after the track change. Figure 2 shows the injury rates before and after the increased track banking. Total injury rates decreased from 8.5 to 6.6 per thousand horse-races (P< 0.05). The rate of minor injuries decreased by 21% from 3.3 to 2.6 per 1000 starters. Major injury or lameness rates decreased by 23% from 5.2 to 4.0 per 100 starters
Although there have been good reasons to expect that an increase in the degree of banking of Standardbred racetracks would reduce injury rates after racing, there has been no evidence to support the argument that racetracks should be redesigned. The results of this study demonstrate that an increase in the degree of banking significantly decreases the rates of injury and lameness. This effect occurs even in the event that the increase was less than optimal for an 800 m racetrack, (5), confirming the opinion that even modest increases in track banking should improve the welfare of Standardbred horses.(3)
These results also suggest that trainers should attempt, whenever possible, to have their horses race and perform fast training exercise on well-banked tracks. Horses that have had previous injury or lameness should preferably be trained on well-banked tracks, because successful rehabilitation may be compromised by exercise on poorly designed tracks.
The 22% decrease in injury rate was unlikely to have been caused by a decrease in speed of the horses during racing. Track records were broken in the period after the track reconstruction in 11 of the 18 classes for which records are kept in pacing and trotting races at Harold Park. The range of decreases in track records was 0.1 seconds (for three year old pacers in 1609 metre races) to 6.1 seconds (for trotters in races over a distance of 2350 metres). The difference in record times for the 18 classes of races was not statistically significant (Mann-Whitney U test).
Other possible explanations for the decrease in injury rates include a change in personnel or routines used by veterinarians or stewards. Most (over 90%) of the veterinary examinations were conducted by the same veterinarian, and there were few changes of personnel on the panel of stewards. As well, there were no rule changes introduced in the period which could explain the result.
It might be argued that the decrease in injury rate could be due to a change in the track usage pattern by trainers with trainers opting to avoid use of the redesigned track for horses which were prone to injury or previously injured. There is no evidence to suggest that this change in attitude or track preference occurred. Indeed, if trainers did perceive that the new track was less stressful on a horse's limbs, as they have elsewhere after similar track redesigns, (3) they may have even been more inclined to race such horses at Harold Park than at other tracks.
The 22% reduction in injury rate is likely to be due to a reduction in the stresses in the legs of horses while they are exercising at high speeds on turns. On underbanked tracks , the legs must, in addition to moving the horse forward, provide a lateral, centripetal force to overcome the inertial forces which would otherwise ensure that the horse travelled in a straight line. On a track with optimal banking, this lateral force is entirely replaced by one normal to the track surface, so that the strain on the horses' legs is equivalent to climbing a slight grade. The horse does not lean in relation to the track surface, and the considerable stresses on the joints, ligaments, muscles and tendons in the legs are avoided.
It is concluded that a change in racetrack construction which increased the banking on turns from 4.8 to 5.7 degrees was associated with a 22% decrease in injury and lameness rate of horses after racing. Such a change in track design to increase the degree of banking helps prevent injury and lameness, and is in the interests of racehorse welfare and the long term success of the harness racing industry.
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