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

Abstract

Many horses, just before and during their athletic career, show vertical movement asymmetries, to the same degree as clinically lame horses. It is unknown whether these asymmetries are caused by pain or have alternative explanations, such as inherent biological variation. In the latter case, movement asymmetries would be expected to be present at a very young age. This study aimed to investigate the prevalence of movement asymmetries in foals. Motion analysis, using an inertial measurement unit-based system (Equinosis), was performed on 54 foals (31 Swedish Warmbloods, 23 Standardbreds) during straight-line trot. The foals were between 4–13 weeks old and considered sound by their owners. Differences between the vertical minimum and maximum values recorded for the head (HDmin, HDmax) and pelvis (PDmin, PDmax) between left and right stance were calculated for each stride and an average was computed for each trial. Thresholds for asymmetry were defined as absolute trial mean >6 mm for HDmin and HDmax, and >3 mm for PDmin and PDmax. These thresholds were exceeded for one or several parameters by 83% of Standardbred foals and 45% of Swedish Warmblood foals, demonstrating surprisingly high prevalence of asymmetries in young foals, although the risk of repetitive strain injuries and cumulative risk of trauma injuries was expected to be low in this age group. Standardbred foals showed similar prevalence of asymmetries to that reported previously for yearling Standardbred trotters, so relatively higher prevalence of movement asymmetries may be expected among trotters as a breed. In general, vertical head and pelvic movement asymmetries can be anticipated among foals considered sound by their owners. A better understanding of the aetiology of asymmetries is needed for correct interpretation of objective symmetry measurements in different populations of horses.

Prevalence of movement asymmetries in high-performing riding horses perceived as free from lameness and riders’ perception of horse sidedness

“…In accordance with previous findings in horses used for general-purpose activities [ 12 , 15 ], polo horses [ 16 ], reining Quarter Horses [ 32 ] and elite eventing horses [ 14 ], the high-performing riding horses in this study displayed a high prevalence (69–70%) of vertical movement asymmetries on both hard and soft surfaces regardless of equestrian discipline, when applying commonly used thresholds. In a group of warmblood foals examined in a previous study, the prevalence of movement asymmetries were lower, with 45% of the foals measuring with asymmetry values above thresholds [ 21 ]. The difference in prevalence of movement asymmetries between foals and older horses could indicate an influence of training or an increasing cumulative risk of injuries with increasing age.…”

“…biological variations such as conformational variations or mechanical restrictions, have been discussed as potential sources for these movement asymmetries [12,14,20]. This is supported by reports of relatively high prevalence of movement asymmetries among young foals [21] and young trotters even before initiation of training [20]. Laterality is another potential cause of movement asymmetries.…”

Inertial Sensor Technologies—Their Role in Equine Gait Analysis, a Review

“…In some cases, subtle lameness and minor gait asymmetry can only be observed when the horse is ridden, performing a certain task, or moving in a certain direction. Moreover, not all asymmetries are caused by lameness [ 64 , 65 ], and not all individuals have the same movement symmetry [ 66 ]. Therefore, the use of IMU systems alone or in combination with subjective evaluation procedures can ensure a comprehensive analysis of horse locomotion under field conditions.…”

Determination of Equine Behaviour in Subjectively Non-Lame Ridden Sports Horses and Comparison with Lame Sports Horses Evaluated at Competitions

“…The development of objective methods of gait analysis and their widespread use in equine lameness assessments and analysis of gaits at pre-purchase examinations have begun to raise questions about what constitutes normality [ 14 , 15 , 16 , 17 , 18 , 19 ]. Measurable gait asymmetries outside the so-called normal ranges [ 20 , 21 ] have been identified in both Warmblood [ 18 ] and Standardbred [ 14 , 18 ] foals and in mature riding horses assumed by the riders to be working satisfactorily at both elite and non-elite levels [ 15 , 16 , 17 , 19 ]. It is not known with certainty whether this reflects innate non-pain induced asymmetry (sometimes referred to as motor laterality) [ 20 , 22 ], which may or may not predispose to subsequent development of pain-related gait changes, or is pain related.…”