The Psychology of Performance Horses

It is common knowledge that a horse must achieve optimal physical fitness in order to deliver a peak performance but what kind of impact does psychological condition have on equine performance? In a competition environment equine athletes in any discipline may show symptoms of stress but to what degree does the expression of that stress affect the quality of a jumping round dressage test reining pattern etc.? And how great is the riders ability to influence either positively or negatively the horses psychological state? 

Recent years have seen these questions become the focus of a growing number of studies on the psychology of performance horses several of which have yielded interesting and applicable results
In the paper entitled Psychological Factors Affecting Equine Performance published in September 2012 in BMC Veterinary Research British researchers Dr. Sebastian McBride from the Royal Agricultural College and Prof. Daniel S. Mills from the University of Lincoln review the current research and confirm that the horses temperament mood and emotional reaction play a significant role in determining equine performance in a competition environment. The authors state that Psychological factors exist at three interrelated but separate levels temperament mood and emotional reaction. Temperament exists as a relatively stable predisposition in adult life which is shaped by genotype and early experience whilst mood describes a more temporary state of psychological functioning which helps to bias behavioural choices toward certain types of action in a predisposing environment. Emotional reactions are the most tightly stimulusbound affective states and the shortest lived thus describing the more immediate response to the subjective evaluation of an event.
Like physical traits an individuals psychological characteristics including temperament are a product of the interaction between the expression of that individuals collection of genes or genotype and the influence of environmental factors. 
McBride and Mills describe the optimal genotype for a horse with respect to both physical and psychological traits as being discipline specific Just as a Shetland will never win the Kentucky Derby so a horse of inappropriate temperament will generally never succeed within a certain discipline. It is therefore essential not only to concisely define the biological basis of temperament but also to identify very carefully which components at the level of both specific behaviours and behavioural predispositions are required to achieve success within a given discipline.
For example Thoroughbreds as a breed may often be described as flighty while Quarter Horses on the whole might be