Resting Concentrations of Cardiac Troponin I in Fit Horses and Effect of Racing

Objectives: To determine normal resting values for cardiac troponin I (cTnI) in healthy Standardbred, Thoroughbred and Warmblood horses and investigate if racing has an influence on cTnI concentrations.

Background: Measuring cTnI concentrations in plasma is the gold standard for detecting myocardial injury in humans. Cardiac troponin I is highly conserved between species and has gained interest as a marker for cardiac injury in horses. Increased levels of cTnI have been reported in association with endurance and short-term strenuous exercise on a treadmill in horses. However, the effect of true racing conditions has not yet been reported.

Animals, Materials And Methods: Blood samples for analysis of cTnI concentrations in plasma were collected from 67 Standardbred racehorses, 34 Thoroughbred racehorses and 35 Warmblood dressage horses at rest. Blood samples were also collected prior to and after racing in 22 Standardbred racehorses and 6 Thoroughbred racehorses.

Results: All horses except one had resting plasma cTnI concentrations <0.022 microg/L. Mild increases in cTnI concentrations were seen in some horses 1-2h after the race (1/17 Standardbreds and 2/6 Thoroughbreds) as well as 10-14 h after the race (4/21 Standardbreds and 1/6 Thoroughbreds).

Conclusions: Resting cTnI concentrations in horses are low but mildly elevated cTnI concentrations may be detected in some horses 1-14 h after racing. These findings could be of importance when evaluating horses with suspected cardiac disease that recently have performed hard exercise.