More than one in five racehorses may be at greater risk of injury when raced in a track direction which goes against their preferred leading leg, according to researchers.
This, in turn, might also be placing jockeys at greater risk, they say.
Researchers have explored laterality in racehorses – examining the race starts of 2095 Thoroughbreds to determine which leg they prefer to lead with when emerging from the starting gates, springing from a standstill into a gallop.
The study team based their findings on the analysis of videos of 350 flat races in Britain, a nation in which horses race clockwise and anticlockwise.
Course direction, horse age and sex, their position relative to the inside rail, and finishing positions were also factored into the analysis work.
Of the 2095 horses studied, 51.26% led with their left front leg and 48.74% led with their right. This was not a statistically significant difference across the study population.
“Therefore, there was no evidence of a population level motor laterality,” Paulette Cully, Brian Nielsen, Bryony Lancaster, Jessica Martin and Paul McGreevy reported in the open-access journal, PLOS ONE.
However, a more detailed breakdown highlighted some interesting patterns.
On clockwise courses, there were more left-leading starts (604) than right-leading starts (527). That amounted to 53.51% favouring the left and 46.49% favouring the right. This was considered a significant difference in proportions between left and right leading starts.
In contrast, there was no significant difference between the number of horses starting on their left or right leg on anticlockwise courses.
Modelling showed that neither clockwise nor anticlockwise course direction was statistically significantly associated with the leading leg of winning horses.
The starting position relative to the inside fence on clockwise courses did not significantly predict the horse’s leading leg. Furthermore, there was no significant relationship between the starting position relative to the inside fence on anticlockwise courses and the horse’s leading leg at the gallop.
Similarly, the age of the horse did not statistically significantly predict the horse’s leading leg.
There was no relationship between the sex of the horse and the horse’s gallop leading leg.
Further modelling was run for stallions, geldings and mares, and no association was found between them with preference for leading leg.
The study team also tested for individual laterality in 44 horses, based on repeated measures, to determine if horses were individually lateralised.
Individually, 43 of the 44 horses exhibited some degree of laterality and one was ambilateral, having equal numbers of left and right leg starts.
Twenty-two of the horses exhibited a trend towards right laterality, two of them significantly so (4.5%). Twenty-one horses exhibited a left laterality, eight of them significantly so (18%).
Of the significantly lateralised horses, there were two right and two left-favouring geldings, four left-favouring females and one left-favouring stallion.
The patterns found pointed to individual preferences, rather than a pattern seen on a wider population basis.
The researchers noted the significant bias toward starting on the left lead on clockwise courses.
“There seems no plausible explanation for different leading leg preferences on clockwise and anticlockwise courses,” they said.
“Given that, over the study period, there were more races in the anticlockwise direction than in the clockwise direction, perhaps experienced horses become accustomed to running to the left.
“This might account for the significant numbers starting on the left lead on clockwise courses but not for the almost equal numbers of horses starting on either the left or right lead on anticlockwise courses.”
From the data on the 44 horses, at least 22.7% were significantly lateralised either to the left or the right.
These animals may be at an elevated risk of injury if raced in a direction contra to what might be considered their innate gallop leading-leg preference, they suggested.
“On bends, it is common for horses to use the left leading leg when galloping in an anticlockwise direction and vice versa.”
They noted that most injuries (72%) occurred to the leading leg of racehorses, irrespective of course direction.
The greater tendency to fracture the left front leg is due to the greater strain put on that leg during turns.
“Also, of injuries sustained to the leading leg, horses are more likely to fracture the foreleg contralateral to the leading leg (that is, the non-leading leg) used for the first few strides of a race.
“This would suggest that the non-leading leg side has either less agility or an underlying weakness.
“Therefore, horses racing on their weaker side, in a direction contra to their preferred leading leg could be at increased risk of injury and wastage.”
The researchers suggested that identifying that a horse is left or right-handed could allow trainers to develop the weaker side and produce a more balanced or ambilateral horse.
“Equally, in countries that race in both directions, such as the UK and Australia, it could allow trainers to prepare strongly biased horses preferentially for races in certain directions.”
It seemed that current training was not conditioning horses to become more ambilateral, they said.
“The role of pain as [a] contributor to motor laterality in the current population cannot be quantified but certainly merits consideration.
“Given that injury during racing is more likely to occur to the non-leading leg used for the first few strides of a race and the leading leg on turns (in both clockwise and anticlockwise directions), the bias reported here may be placing horses and jockeys at risk.”
Cully, Lancaster and Martin are with the University of Edinburgh; Neilsen is with Michigan State University; and McGreevy is with the University of Sydney
Cully P, Nielsen B, Lancaster B, Martin J, McGreevy P (2018) The laterality of the gallop gait in Thoroughbred racehorses. PLoS ONE 13(6): e0198545. https://doi.org/10.1371/journal.pone.0198545