Study on Changes in Racehorses' Metabolites and Exercise-related Hormones before and after a Race

Physiological changes in thoroughbred racehorses during the race were investigated by measuring concentrations of metabolites and exercise-related hormones before and after a race. The conversion point from anaerobic to aerobic exercise during the race was estimated subsequently. Blood samples were taken from the jugular vein of 53 thoroughbreds at different times -three h before and 45 min after- for measuring the concentrations of glucose, non-esterified fatty acids (NEFA), lactate, uric acid, ammonia, insulin, adrenocorticotrophin (ACTH) and cortisol according to the race distance. In accordance with the race distance, each metabolite increased in concentration compared with the level before the race. The level of glucose, in particular, increased from $56.18{\pm}3.20$ mg/dl before the race to $148.82{\pm}8.82$ mg/dl after the race for horses that raced 1,400 m, showing a significant increase of 165% (p<0.001). The concentration of NEFA rose from $76.77{\pm}5.59$ uEq/L to $335.85{\pm}35.39$ uEq/L, up 337% (p<0.01) after a 1,400 m race. Exercise-related hormones also showed similar changes. The level of insulin dropped the most in horses that raced 1,400 m, by 42%, from $0.97{\pm}0.18$ to $0.56{\pm}0.05\;{\mu}g/L$ (p<0.5); however, ACTH and cortisol jumped significantly at 1,800 m, from $20.17{\pm}2.12$ to $551.45{\pm}91.33$ pg/ml (p<0.5) and $1.13{\pm}0.16$ to $5.66{\pm}0.45\;{\mu}g/dl$ (p<0.01), respectively, representing the highest increase. Therefore, based on the changes in glucose, NEFA and insulin levels before and after the race, it was concluded that the race distance of 1,400 m represents the point where racehorses make a conversion from anaerobic to aerobic exercise.