Trot asymmetry in relation to physical performance and metabolism in equine endurance rides

Trot is a symmetric gait and asymmetry might appear or increase during endurance rides due to lameness, pain or excessive fatigue.

To assess whether trot asymmetry increases during endurance competitions, whether it is possible to discriminate between horses with different performance and also its possible relationship with metabolism.

Fifty-eight horses were filmed at trot during the lameness examinations in the vet-gates, before the competition (BCO), and after phases 1 (at 29 km), 2 (at 59 km) and 3 (at the end of the ride, at 80 km) and stride duration (SD) measured in all 4 limbs. A locomotion symmetry index (LSI) was calculated by comparing SD in the diagonal pairs of limbs. In all the cases, the longer diagonal pair SD was compared to the shorter. Horses were classified as symmetric (SyH) when LSI was lower than mean + 2s.d. and asymmetric (ASyH) when LSI was higher than mean + 2s.d. of the data obtained in BCO. Venous samples were withdrawn in the vet-gates and PCV, WBC, creatinine, TPP, uric acid, CK, AST, LDH, Na, K and Cl were measured. Horses were divided into different performance groups: successful (SH), lame (LH) and metabolic (MH), and according to ride velocity, the SH group was also divided into faster finishers (FF) and slower finishers (SF).

The percentages of SyH were high (>80%) and very similar between the different performance groups. LSI became more asymmetrical in the vet-gates, especially in the LH and MH groups. LSI presented negative correlations with the velocities during the rides and in the vet-gates and CK. The ASyH had higher velocities during the rides and plasma CK and lower velocities during the vet-gates and plasma uric acid concentrations.

Although trot asymmetry increases during endurance events, LSI calculated comparing SD in the two diagonal pair of limbs did not allow the differentiation of horses with different performance.