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.

In equine sports, the rate of recovery after an exhaustive exercise session greatly affects the ability of the animal to perform subsequently, especially if the next exercise session occurs quickly. Carnitine participates in fatty acid delivery to the mitochondria and may facilitate muscle recovery post-exercise. The objective of the study was to determine the effects of a commercially available carnitine supplement (Renew, Platinum Performance, Buellton, CA) on adult The ability of Thoroughbred horses (16 geldings, 2 mares, 6.69 ± 0.49 years, 524.81 ± 10.07 kg, 5.66 ± 0.12 BCS) to perform successive bouts of exhaustive exercise. All horses participated in a moderate workload conditioning program for 6-weeks before testing. Horses received a ration of applesauce (30 mL, CON, n = 8) or ration of applesauce containing 19.6 g of the product (30 mL, AID, n = 8) 1 h before performing an incremental standardized exercise test (iSET) to exhaustion (day 1). Heart rate (HR) and gait biomechanics were recorded throughout the duration of the iSET. Blood was collected at 0, 10 min, 1, 4 and 6 h relative to exercise for the measurement of lactate and interleukin (IL) 1b, 8 and 10 mRNA content. for the measurement of lactate and interleukin (IL) 1b, IL8 and IL10 mRNA content. The AID was administered again at 1 h post-iSET after collection of the blood sample. All horses were rested for 24 h before repeating the iSET (day 3) with performance data and sample collection. The AID did not affect time to maximum HR, time to reach V200 or total gallop time during the iSET on day 1 or day 3. The rate of HR decline post iSET was slower (P &lt; 0.05) for all horses on day 3 compared with day 1. Blood lactate concentration was not affected by AID or day. The right front limb posterior fetlock angle at full stance phase increased (P &lt; 0.05) with speed for both CON and AID supplemented horses on day 1. Horses receiving AID demonstrated an increase (P &lt; 0.05) in this measure at day 3 while no significant differences (P &gt; 0.05) in posterior angle were detected in CON. Administration of AID did not affect whole blood IL1b, IL8 or IL10 mRNA content on day 1 or day 3. Consolidation of the data demonstrates increased (P &lt; 0.05) expression of IL1b and IL8 mRNA during post-exercise recovery time on day 1 that was absent on day 3. Expression of IL10 was altered (P &lt; 0.05) over time post-exercise on both days. Results of the experiment demonstrate that successive bouts of exercise affect the inflammatory response to exhaustion. Although AID did not affect IL gene expression, it did promote retention of flexion at the fetlock joint suggesting that carnitine products may facilitate recovery from strenuous exercise.