Some factors influencing plasma AST/CK activities in thoroughbred racehorses.

This study examines factors that affect the plasma AST/CK activities in Thoroughbred racehorses. Factors considered include age, sex, time of year, and dietary electrolyte imbalances. The results show that sex and age significantly affect plasma AST/CK activities, while time of year does not.

Study Design and Participants

• The study was conducted during one flat racing season and included 66 Thoroughbred horses that were either two or three years old. All horses were in training.
• The researchers aimed to minimize the effects of different training and management methods on the outcomes of the study.

Data Collection

• Post-exercise samples were collected monthly from February to October. These samples were analyzed for aspartate aminotransferase (AST) and creatine kinase (CK) activities.
• The dietary intake of calcium, sodium, phosphorus, and potassium was recorded each time a sample was collected.
• Eight of the horses had the fractional electrolyte excretion (FE) levels of phosphate (PO4) and sodium (Na) measured monthly.
• Three horses, which had suffered repeated episodes of equine rhabdomyolysis syndrome, also had their FE, PO4, and Na levels measured.

Study Findings

• The study found that a horse’s sex and age significantly affected its CK and AST activity levels. Fillies (female horses) were more likely to have elevated CK and AST activity levels than colts (male horses). Additionally, two-year-old horses were more likely to have higher AST activity levels than three-year-old horses.
• The the time of year did not affect the number of horses with high or low CK and AST activity levels.
• Fourteen horses had consistently high AST activity levels (median > 300 iu/litre). Of the eight that raced, seven won at least one race.
• The FE, PO4, and Na values mirrored the dietary intake of calcium, sodium, and phosphorus respectively.
• The study did not find any effect of training or a predisposition to equine rhabdomyolysis, a disease characterized by muscle breakdown and damage.
• There were no apparent differences in the resting thyroxine values of horses with consistently low AST activities, high AST activities, and horses that had suffered from rhabdomyolysis.