Assessment of drug effects on performance

Few definitive studies have been performed that unequivocally demonstrate the ability of a drug to alter the performance of a horse. Nonetheless, the use of drugs in competing horses is regulated worldwide. Drugs have been categorized according to their abuse potential. However, there is still some confusion over what is meant by the terms "performance" and "drug." In the racing community, performance means speed, and fatigue and pain are among its greatest detractors. Speed is most appropriately measured on the racetrack. There are a multiplicity of internal and external variables that influence a horse's racetrack performance. Consequently, it is difficult to show drug-induced changes in speed, experimentally, on the racetrack. However; rigorous experimental designs and larger numbers of horses may enhance the value of this approach. High-speed equine treadmills provide a modified racing laboratory environment. A number of performance-related variables such as heart rate, oxygen consumption, and lactate production can be measured, and correlations with actual performance times have been shown. Drug-induced changes in some of these variables have been demonstrated. Behavioral pharmacology techniques have been adapted to the horse. Finite changes in spontaneous locomotor activity and pain perception have been demonstrated following the administration of putative stimulants, depressants, and anesthetics. Precise onset, duration of action, and potency of the various agents can be determined using this approach. Drug-induced changes in heart and respiratory rates in laboratory horses at rest also may be of some predictive value. Retrospective studies of racing times in medicated horses have yielded some interesting results. At the present time, the regulatory science of "doping control" is still heavily reliant on inference and extrapolated knowledge of human and equine pharmacology.