Correlation Between Serum Activity of Muscle Enzymes and Stage of the Estrous Cycle in Italian Standardbred Horses Susceptible to Exertional Rhabdomyolysis.

This research explores how muscle enzyme activity in racehorses changes with the stages of their reproductive cycles, and how this might contribute to a susceptibility in female horses to exertional rhabdomyolysis (ER), a muscle disorder associated with strenuous exercise.

Overview of the Research

• The study focused on equine exertional rhabdomyolysis (ER), a muscle disorder that is more prevalent in female racehorses. It aimed to understand how the activity levels of muscle enzymes in these horses change across different stages of their reproductive (estrous) cycle, and whether these changes relate to their susceptibility to ER.

Study Design and Methodology

• A total of 20 mares were included in the study: 10 that were susceptible to ER (the test group) and 10 controls. These mares were observed over a period of four weeks.
• Researchers monitored the horses’ muscle enzyme activity levels and sex hormone levels throughout the cycle, both at rest and after exercise.
• A particular focus was placed on two muscle enzymes: aspartate aminotransferase (AST) and creatine kinase (CK) which were studied before and after exercise.

Research Findings

• In the diestrus phase (non-receptive to the mating), the ER-group mares showed significantly higher resting and postexercise AST levels than the control-group mares. However, no significant difference was observed in the CK levels of the two groups.
• In the estrus phase (receptive for mating), only the post-exercise AST levels in the ER-group mares were found to be significantly higher compared to the control group.
• The research also found a significant negative correlation between the levels of the female hormone 17β-estradiol and AST activity in the control group mares during the estrus phase, but not in the ER-group mares.

Implications and Suggestions for Future Research

• The findings suggest that sexual hormones might have different effects in healthy mares compared to those susceptible to ER. Further research is needed to understand the varying roles these hormones play in these different groups of horses.
• This study could inform efforts to better manage and possibly prevent exertional rhabdomyolysis in racehorses, particularly in female horses that show a susceptibility to the condition.