A Carnitine-Containing Product Improves Aspects of Post-Exercise Recovery in Adult Horses

SIMPLE SUMMARY: Horses performing strenuous exercise can experience tissue damage, causing a delayed return to work. L-Carnitine supplements may accelerate the post-exercise recovery period, allowing for an earlier return to work. Adult Thoroughbreds were administered a commercial carnitine-containing recovery aid prior to performing exercise to exhaustion (D1). The activity was repeated after a single day of rest (D2), with physiological and biochemical measures obtained following exercise on both days. The results demonstrate that horses receiving the L-carnitine-containing supplement retained a greater range of motion in their fetlock on D2 than the controls. A normal inflammatory response to exercise was observed for all horses on D1, which was not found on D2; the heart rate recovery on D2 was also slower. These results indicate that a single day between strenuous work is insufficient to allow for tissue recovery. ABSTRACT: Strenuous exercise can cause tissue damage, leading to an extended recovery period. To counteract delayed post-exercise recovery, a commercial product containing L-carnitine (AID) was tested in adult horses performing consecutive exercise tests to exhaustion. Fit Thoroughbreds were administered an oral bolus of placebo (CON) or AID prior to performing an exercise test to exhaustion (D1). The heart rate (HR) and fetlock kinematics were captured throughout the exercise test. Blood was collected before, 10 min and 1, 4 and 6 h relative to exercise for the quantification of cytokine (IL1β, IL8, IL10, TNFa) gene expression and lactate concentration. Horses performed a second exercise test 48 h later (D2), with all biochemical and physiological measures repeated. The results demonstrate that the horses receiving AID retained a greater (p < 0.05) amount of flexion in the front fetlock on D2 than the horses given CON. The horses presented a reduced (p < 0.05) rate of HR decline on D2 compared to that on D1. The expression of IL1β, IL8 and IL10 increased at 1 h post-exercise on D1 and returned to baseline by 6 h; the cytokine expression pattern was not duplicated on D2. These results provide evidence of disrupted cytokine expression, HR recovery and joint mobility in response to consecutive bouts of exhaustive exercise. Importantly, AID may accelerate recovery through an undetermined mechanism.