Blood chemistry and skeletal muscle metabolic responses during and after different speeds and durations of trotting

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Abstract
Summary: Eight standardbred horses trotted on a treadmill for 55 mins at a sub‐maximal speed of 5m/sec and subsequently performed an exercise test consisting of 2 min intervals at increasing speed. Heart (HR) and respiratory (Rf) rates and venous blood samples were obtained before, during and for 5 mins after exercise. Gluteus medius muscle biopsies and rectal temperatures were taken before and after exercise. The mean HR was 132/min and the mean Rf was 156/min during the 5m/sec trotting. With 5m/sec exercise, plasma free fatty acids (FFA), glucose, creatinine and Cortisol concentrations increased markedly. Blood lactate increased slightly and plasma potassium increased initially and then decreased with a lengthened duration of trotting. Within 5 mins post exercise plasma FFA, glucose and Cortisol concentrations continued to rise, whereas creatinine and lactate levels declined slightly and potassium concentrations declined rapidly to below resting values. The mean intramuscular (im) glycogen utilisation was 86 mmol/kg, no significant changes occurred in creatine phosphate (CP), adenosine triphosphate (ATP) and glucose‐6‐phosphate (G‐6‐P) concentrations and muscle lactate decreased significantly. During the second exercise test mean HR was 215/min and Rf 126/min at top speed. No significant change was seen in plasma glucose whereas Cortisol levels rose to a lesser extent, and creatinine lactate, ammonia and potassium concentrations to a greater extent, compared to 5 m/sec trotting. Post exercise, these parameters continued to increase except for creatinine which declined slightly and potassium which decreased rapidly. The mean im glycogen utilisation was 144 mmol/kg, ATP concentrations were unaltered, CP declined, lactate and G‐6‐P increased during exercise. The rapid changes in concentrations of blood chemistry parameters post exercise emphasise the importance of obtaining blood samples during exercise when studying metabolic response.