| dc.description.abstract | Blood lactate concentrations and heart rate levels surrounding exercise provide valuable insight into the physiological response to advancing workloads, but minimal research has been published involving yearling horses. Therefore, the objective of the study was to determine blood lactate and heart rate response to increasing exercise intensity in yearling horses. It was hypothesized that blood lactate levels would peak immediately following exercise, and gradually decrease over a 3 h post-exercise period. Comparatively, heart rate levels would increase over time in response to an increasing exercise intensity. To test this, 32 Quarter horses of similar background (480-520 d of age; 16 geldings and 16 fillies) were randomly assigned to one of four groups (n=8/group) and exercised using an 8-panel free-stall walker. Exercise bouts ranged between 30-45 min and were divided equally in the clockwise and counterclockwise directions. Each wk, 4 horses per group were randomly assigned and equipped with onboard heart rate monitors during exercise each d throughout the course of this study. Blood lactate measurements were taken at the beginning of an increase in exercise intensity, noted as Test 1, Test 2, and Test 3. Test 1 consisted of walking at 1.75m/s, Test 2 consisted of horses alternating between the walk and trot at 1.75 and 4.0 m/s and Test 3 consisted of horses alternating between the walk, trot, and canter at 1.75, 4.0. and 6.0 m/s respectively. Blood samples were obtained at the onset (PRE) and immediately (H0), half (H0.5), one (H1), and three (H3) h post-exercise. Heart rate levels were continuously monitored throughout the course of exercise. Mean blood lactate was determined using two portable lactate analyzers previously validated for use in horses. Data were analyzed using PROC MIXED of SAS with PRE-blood lactate values used as a covariate, and no covariate was used for heart rate data. Heart rate increased over time (P <0.01) in response to an increasing exercise intensity. There was a group × test × time interaction (P<0.01), where Group 3 reached peak lactate concentration at H0 during Test 2, while all other groups increased blood lactate concentrations over time to H3 post. Mean lactate (1.07 ± .08 mmol/l) post-exercise indicates that horses were able to clear lactate without a sufficient increase in systemic distribution. During Test 2, mean lactate for Group 3 peaked at H0 (1.23 ± .08 mmol/l) with a gradual decrease during recovery. Although there was an increase in heart rate levels over the course of the study, mean heart rate remained within sub-maximal values. Lactate concentrations varied across all three tests, but all values remained below the anaerobic threshold, similar to mature horses, which suggests that sub-maximal exercise in young horses does not elicit an anaerobic response and lactate accumulation. | |
