Locomotion asymmetry in young Standardbred trotters in training and links to future racing career

Abstract

This study evaluated whether front and hind limb symmetry patterns observed from 1.5 through 3 years of age in Standardbred trotters in training affect racing activity at older age. The hypothesis tested was that asymmetries observed during this period are linked to reduced number of lifetime races and low earnings. Sixteen Standardbreds were subjected to a controlled training and dietary programme from the age of 1.5 years until December as 3-year-olds (P1) and then continued their career with other trainers. On 17 occasions during P1, locomotion asymmetry (vector sum) in front and hind limbs during trot in hand was recorded with a sensor-based system. By 10 years of age, data on lifetime number of races and earnings of the horses were obtained from the Swedish Trotting Association. Horses were divided in groups based on the number of lifetime races performed, i.e. more or less than the median of the cohort born the same year. Mean asymmetry levels did not differ between horses performing more or less lifetime races than the cohort median. However, horses that showed the poorest lifetime race activity showed elevated hind limb asymmetry in August at the age of 3 years, compared to horses with more races (group <median: 9±6 mm vs group >median: 6±2 mm (P=0.02)). There were no correlations between individual mean and peak asymmetries and lifetime earnings. It is concluded that locomotion symmetry observed during trot in hand at the age of 1.5-year-olds to December as 3-year-olds was not a simple and straight-forward predictor of future racing career. However, hind limb asymmetries of around 10 mm in the late season as 3-year-olds could be a warning of impaired future performance.

Prevalence of vertical movement asymmetries at trot in Standardbred and Swedish Warmblood foals

“…Taking the above into consideration, the individual horse might well serve as its own reference for evaluating objective movement measurements when not related to suspicion of lameness. The availability of smartphones and ongoing rapid technological advances may soon make it possible for owners to track their horses´ movements [ 44 ] and detect irregularities in the movement “pattern” for that specific horse [ 15 ]. The aim in the present study was to describe and present the prevalence and magnitude of movement asymmetries in foals and not to draw conclusions regarding underlying causes.…”

“…Age, use and management of these populations vary greatly, from yearlings before initiation of training to adult horses in training. The high prevalence of vertical movement asymmetries in populations of horses in regular training [ 10 , 11 , 15 ] raises the question of unrecognised lameness and a potential welfare issue. However, the clinical significance of these asymmetries in apparently sound horses remains unclear and other explanations, such as inherent biological variation, have been proposed [ 11 , 16 ].…”

Rein tension in harness trotters during on-track exercise

“…Above threshold movement asymmetries at trot, potentially indicative of lameness, are very common both in riding horses ( 29 ) and in young trotters ( 30 – 32 ) considered sound by their owners. The relationship between motion symmetry and performance appears relatively weak, but horses that showed the poorest lifetime race activity tended to show elevated hind limb asymmetry ( 32 ).…”

“…Above threshold movement asymmetries at trot, potentially indicative of lameness, are very common both in riding horses ( 29 ) and in young trotters ( 30 – 32 ) considered sound by their owners. The relationship between motion symmetry and performance appears relatively weak, but horses that showed the poorest lifetime race activity tended to show elevated hind limb asymmetry ( 32 ). In the current study, if the horse was hind limb asymmetric, this was associated with substantially increased median rein tension, from 28 N to 48 N. Similarly, maximum values increased from 71 N to 104 N. The immediate cause of this relationship remains unclear, but perhaps horses with a more unstable gait have an increased tendency to seek support by hanging on the bit.…”