The Level of Thiol-Oxidised Plasma Albumin Is Elevated Following a Race in Australian Thoroughbred Horses

Abstract

Background: The extent to which muscle strain or tears are affecting race performance in horses is unknown because it is difficult to objectively identify muscle damage. One approach includes the use of physiological markers in blood. Recently, we linked the level of plasma thiol-oxidised albumin, an oxidative stress biomarker, to muscle damage in humans.

Objectives: This aim of this work was to investigate whether the level of plasma thiol-oxidised albumin was elevated in the days following a thoroughbred horse race.

Study design: 'In vivo' experiments.

Methods: Blood collection was performed by each trainer at their respective stable. Dried blood samples were collected for the level of thiol-oxidised albumin before and each day for 7 days post-race. Liquid blood samples were collected for analysis of the muscle enzymes creatine kinase (CK) and aspartate amino transferase (AST) before and on Day 2 and 5 post-race and were analysed by external pathology centre.

Results: The level of thiol-oxidised albumin peaked at 2 days post-race, increasing by 3.9 ± 0.7% (p < 0.0001) and returned to pre-race levels by Day 5. Thiol-oxidised albumin also correlated with the activity of AST (R² = 0.2, p = 0.01). The time of recovery for thiol-oxidised albumin varied between individual horses, some recovered at Day 3 post-race whereas others extended beyond 7 days post-race.

Main limitations: No histological or imaging diagnosis was conducted to confirm that horses with elevated levels of thiol-oxidised albumin also had definitive evidence of muscle damage. The activity of CK and AST was not measured daily, as was the case for the level of thiol-oxidised albumin.

Conclusions: The level of thiol-oxidised albumin has the potential to be useful in managing recovery and return to training or competition in horse following a bout of damaging exercise, particularly given the ease of collecting small serial small blood samples.

Keywords: muscle damage; oxidative stress; physical exercise; thiol‐oxidised plasma albumin; thoroughbred horse; training.

FIGURE 1

Representation of study testing schedule. A cohort of 46 horses were sampled for the level of thiol‐oxidised albumin on subsequent, alternating days at the conclusion of their pre‐race training period when they were ready to race but have not yet raced (race‐fit baseline). A separate group of 34 horses were sampled for the level of thiol‐oxidised albumin at 48 h before a race and each day for 7 days after a race. At both 48 h before the race and on Days 2 and 5 post‐race, each horse underwent an additional blood draw for analysis of CK and AST.

FIGURE 2

Absolute levels of total thiol‐oxidised albumin, reversible thiol‐oxidised albumin and irreversible thiol‐oxidised albumin for each day of the baseline testing period. Data are means ± 95% CI. n = 46 horses.

FIGURE 3

Absolute level of irreversible thiol‐oxidised albumin for the post‐race testing period. Pre represents 24 h prior to the race. Data are means ± 95% CI. n = 11 horses.

FIGURE 4

Absolute level of total thiol‐oxidised albumin for the post‐race testing period. Pre represents 24–48 h prior to the race. Data are means ± 95% CI. ****Significantly different from pre‐race p < 0.0001, **p < 0.01, *p < 0.05. n = 34 horses.

FIGURE 5

Changes in the level of total thiol‐oxidised albumin for the post‐race testing period. Pre represents 24–48 h prior to the race. Data are expressed relative to the pre‐race baseline value of 0% and are means ± 95% CI. ****Significantly different from pre‐race p < 0.0001, ***p < 0.001, **p < 0.01, *p < 0.05. n = 34 horses.

FIGURE 6

Absolute levels of (a) creatine kinase (CK) and (b) aspartate amino transferase (AST) before (pre) and after a race. Data are expressed as means ± 95% CI values for both CK and AST. n = 20 horses.

FIGURE 7

Heatmap depicting the level of thiol‐oxidised albumin that was below the reference change value or above the reference change value for 34 horses using a confidence of 99% each day following a race.