Effects of flunixin on cardiorespiratory, plasma lactate and stride length responses to intense treadmill exercise in Standardbred trotters.

The research studies the effects of a nonsteroidal anti-inflammatory drug, flunixin, on the physiological parameters of Standardbred trotter horses during intense treadmill exercise. The findings indicate that flunixin influences responses to exercise but does not enhance the athletic performance of healthy horses.

Objective and Methodology

• The primary objective of this study was to investigate the effects of a nonsteroidal anti-inflammatory drug named flunixin on various parameters related to cardiorespiratory, metabolic, and locomotive functions in horses during intense treadmill exercise. There was a particular interest in how such drugs might influence the physiological responses to exercise and, possibly, performance potential in equestrian sports.
• The study used six Standardbred trotters for a test of incremental treadmill exercise until fatigue. The test was first conducted without drug intervention and then repeated after administering a dose of flunixin meglumine (1.1 mg/kg bwt i.m.). During the test, heart rate (HR), oxygen consumption, stride length, and plasma lactate concentration were measured multiple times.

Results

• The results showed higher heart rates at submaximal speeds and lowered velocity at which a heart rate of 200 beats per minute was achieved, after the horses were treated with flunixin.
• Interestingly, maximal heart rate and post-exercise plasma lactate concentration (measured after 5 minutes) remained unaffected by the drug treatment.
• Flunixin was found to cause higher plasma lactate concentrations at all speeds, indicating a lower lactate threshold compared to that of the baseline measures.
• Oxygen uptake remained constant even at maximum velocities, regardless of whether the horses were treated with flunixin.
• Stride length showed an increase with flunixin treatment, but this effect wasn’t evident at maximum velocities.

Conclusions

• Based on the results, flunixin does influence certain physiological responses in horses during exercise, including elevated heart rate and lactate levels.
• However, crucially, the study concluded that flunixin does not enhance the performance potential of clinically healthy horses, even though it may affect certain physiological parameters.
• The study further suggests that the observed increase in stride length during submaximal exercise after medication could indicate subclinical lameness that was masked by the drug in some horses. In other words, while the stride was longer, it was achieved at the cost of higher heart rates and increased lactate concentrations, possibly indicating distress or discomfort.