Motion asymmetry and body fat in Swedish riding school horses : is there a connection?

Abstract: In Sweden, there are about 18 000 riding school horses and in 2018 almost five million riding hours took place in Swedish riding schools. A recent study found that overweight is common in riding school horses, 28 % had a BCS ≥ 7. It has been reported that the prevalence of overweight and obesity in the equine population has increased worldwide. If the horse is overweight or obese there is an increased risk for various health problems. In humans it has been found that obesity is a risk factor for both hip and knee osteoarthritis. A connection between obesity and osteoarthritis is not well documented in horses. However, lameness is the most common cause for veterinary care and life insurance claims for Swedish riding schools. This master’s thesis aim is to analyse if there is a relationship between a high body condition score and motion asymmetry in Swedish riding school horses. Body condition score (BCS), cresty neck score, subcutaneous fat, heart girth circumference and motion asymmetry were measured in 109 riding school horses in the current study. Body condition was assessed with a nine-point scale and cresty neck score was assessed with a five-point scale. Subcutaneous fat was measured with ultrasound at two locations on the rump. The measured thickness was used to estimate percent body fat. Motion asymmetry was measured objectively by the inertial sensory system Lameness Locator. The horses were trotted at hand in a straight line for approximately 100 meters. The maximum and minimum position for both head and pelvis were used to calculate vector sums. A questionnaire was sent to the participating riding schools and questions about their routines and the horses’ temper were asked. Statistical analyses of motion asymmetry and questionnaire answers were made in SAS 9.4 and multiple linear analyses of variance were made using the GLM procedure. Correlations for all included parameters were made with the PROC CORR procedure. BCS was not significantly correlated with percent body fat. BCS did not have an effect on front limb asymmetry (P > 0.05) but a tendency for an effect on hind limb asymmetry (P = 0.09). In the correlation analysis the higher the BCS the more asymmetric hind limb motion (r = 0.18, P = 0.06). There were no significant differences in motion asymmetry between horses with a BCS < 6 and horses with a BCS ≥ 6 or in horses with < 10 % body fat and horses with ≥ 10 % body fat. Percent body fat did not affect front limb asymmetry but had a tendency to affect hind limb asymmetry (P = 0.08). Asymmetry in both front and hind limbs had a weak negative correlation with subcutaneous fat thickness measured 15 cm from the apex of the croup towards the tailhead (front limb asymmetry: r = -0.19, P < 0.05 and hind limb asymmetry: r = -0.21, P < 0.05). Asymmetric movement in hind limbs had a weak negative correlation with percent body fat (r = -0.20, P < 0.05). Number of lessons a horse was used per week did not affect motion asymmetry. Horses that spent < 11 h/day outside were less asymmetric in front limbs compared to horses that spent > 11 h/day outside (P < 0.05). Horses with a BCS < 6 scored higher for how willing a horse was to work and how energetic the horse was compared to horses with a BCS ≥ 6. The results of this study showed no significant relationship between body condition score and motion asymmetry in riding school horses but there was a statistical tendency for horses with higher body condition score to be more asymmetric in hind limbs. However, there were also conflicting results as horses with higher percent body fat were less asymmetric in hind limbs. More studies need to be done in this area to see if BCS affects the motion pattern of horses. Future studies should include a larger study material and more background data about the horses’ health.