The effect of breed, sex, age and race type on racing performance and blood myostatin, irisin, erythropoietin levels in thoroughbred and arabian horses

Objective: This study was conducted to determine the effects of some biological and environmental factors such as breed, sex, age and race type on the blood myostatin, irisin and erythropoietin levels and racing performance in Thoroughbred and Arabian horses. Materials and Methods: The study was conducted on 176 racehorses (88 Thoroughbred, 88 Arabian Horse) participating in official races organized by the Turkish Jockey Club at İzmir Şirinyer Racecourse, and myostatin, irisin and erythropoietin levels were determined in serum obtained from blood samples taken from the horses before the race using the ELISA method. Data on the racing performance of horses were obtained from the Turkish Jockey Club database; the effects of track type, track length, racing age, ranking status and seasonal factors on speed, myostatin, irisin and erythropoietin levels were analyzed using the general linear model method. Results: The findings obtained in this study revealed that there was a statistically significant difference in terms of racing performance between Thoroughbred and Arabian horses, but that gender differences within the same breed did not have a significant effect on speed. It was determined that the type of track had an effect on the speed factor; horses running on grass tracks reached higher speed values than those running on sand tracks. Myostatin levels were significantly higher in the horses that won the championship, providing important clues that this myokine may be related to performance. It was determined that myostatin and irisin concentrations showed seasonal variation and that these differences were statistically significant. Irisin levels were also affected by environmental factors; higher levels were observed especially in horses running on turf tracks and this difference was found to be statistically significant. Although numerical differences were observed between the groups in terms of erythropoietin levels, these differences did not reach statistical significance. In addition, significant differences were found in speed and irisin levels depending on the age of racing; although statistical significance could not be obtained in myostatin levels, remarkable numerical differences were determined. Conclusion: This study is an original investigation that examines the effects of biological and environmental factors such as breed, sex, age, and race type on racing performance and circulating levels of myostatin, irisin, and erythropoietin in Thoroughbred and Arabian horses. The findings revealed that age has a significant impact on both speed and certain biomarker levels, while myostatin and irisin concentrations were found to be sensitive to factors such as season, track type, and performance status. Moreover, the significant positive correlation identified between myostatin and irisin suggests a possible shared regulatory mechanism of these two myokines in exercise physiology. The results provide valuable insights for understanding the physiological condition of racehorses and for the biomarker-based evaluation of performance. As one of the first comprehensive studies conducted in this field in Türkiye, the research offers a novel contribution to the existing literature. Keywords: Thorougbred Horse, Arabian Horse, racing performance, speed, myostatin, irisin, erythropoietin