Motion asymmetry in Swedish riding school horses : association to management factors

Abstract: Orthopedic disorders and injuries have a huge impact on horses, globally as well as in Sweden, and is a common reason for euthanasia in equine veterinary practice. Lameness is the most common sign of orthopedic pain and does not only come with welfare issues but also huge economic consequences. Riding school horses represent an important part of the Swedish horse industry, and 10 700 horses were active in Swedish riding schools in 2019. Previous studies found differences in orthopedic health status between riding schools, which were suggested to be associated with the riding schools’ management and individual horse factors. The purpose of this master´s thesis is to further describe motion asymmetry (by objective evaluation), management factors, and horse factors in Swedish riding school horses. Four of the 14 contacted riding schools participated in the current study, with a total of 76 horses. Management and horse factors were investigated by questionnaires answered by the riding school managers. Motion symmetry was objectively measured with the markerless smartphone app Sleip AI, which uses artificial neural networks to identify vertical motion asymmetry. The horses were recorded trotting in-hand in a straight line on packed dirt 30 meters two times back and forth (approximately 120 meters in total). Each horse was measured on two or three different occasions, with 7-8 days in between. Lameness metrics; HDmin, HDmax, PDmin, and PDmax were extracted from each horse’s asymmetry measurement. A representation of the horse’s total amount of motion asymmetry was calculated by adding these four values together from each measurement occasion and then a mean value from all measurement occasions was calculated. The mean total asymmetry was used in descriptive statistics and for hypothesis testing. A horse was defined as having a relevant total motion asymmetry when the value was >0.75. This was based on clinical experience. Hypothesis testing was performed by grouping horses based on age, gender, number or hours of riding lessons per week, months since the acquisition, previous lameness, summer rest, and type of activity, and by using a double-sided heteroscedastic t-test to investigate differences in total motion asymmetry between groups. The level of significance was set to p< 0.05. Results showed that in the four riding schools the total motion asymmetry ranged from 0.30 to 2.20, and 50 of the 76 horses (66%) were considered to have relevant (>0.75) motion asymmetry. A significant difference in total motion asymmetry was found between horses in groups based on the amount of summer rest in one riding school (p=0.004), the number of riding lessons per week (p=0.017 and p=0.034), and previous lameness (p=0.02) for all riding schools together. No significant difference in total motion asymmetry was seen between horses in groups which were based on hours of riding school lessons, type of activity, age, gender, breed, and time since acquisition. But through descriptive statistics, (non-significant) differences in total motion asymmetry within the studied horse sample were seen between subgroups based on the type of activity, age, and time since acquisition. Further, variance in the lameness metrics HDmin, HDmax, PDmin, and PDmax was observed (but not further investigated) between measurement occasions. Some horses were observed to repeatedly show asymmetry from the same limb, while in others the origin of the asymmetry differed between the measurement occasions. The results from this study indicate that differences in riding school horses’ motion asymmetry can be associated with management and horse factors. The results support that specific attention should be given to the amount of summer rest, the number of riding lessons per week, and previous lameness, but likely other management- and horse factors can be of importance too. This agrees with previous literature concerning riding school horses’ orthopedic health status in Sweden. With that being said, additional studies are needed in this field to draw robust conclusions. Further studies should include larger study material and follow the horses' motion symmetry over a longer period of time. Also, more management and horse factors that possibly can affect the horses' motion symmetry should be included.