In Rollkur, the horse's neck is hyper flexed so that the nose is very close to, if not touching, the chest. The front of the head is behind the vertical (angled in) instead of being vertical or slightly forward of vertical as in normal poll flexion.
Dr Ute von Borstel and others working at the University of Guelph in Ontario, Canada conducted a series of tests to investigate whether the technique adversely affects the horse's welfare.
The FEI's draft description of Rollkur states that: "Hyperflexion of the neck is a technique of working/training to provide a degree of longitudinal flexion of the mid-region of the neck. Hyperflexion cannot be self-maintained by the horse for an extended period of time."
With the help of two equestrian centres - one in Ontario, the other in Ohio - the researchers devised a preference test, to see if horses would choose or avoid Rollkur if they had the choice.
Equine Science Update e-news reports that each horse was ridden into the trunk of a Y-shaped maze and allowed to choose which arm of the maze to take to enter an exercise area. After leaving the maze the horses would be ridden in 20 metre circles in either the Rollkur or normal poll flexion posture, depending on which arm of the maze they had chosen.
Previous training had taught the horses that leaving through the left arm would result in being ridden in the Rollkur posture. Leaving through the right arm resulted in being worked in a normal outline.
A rider would ride the horse into the maze, but allow the horse to choose the exit - and by implication the style of riding that would follow.
Fourteen of the 15 horses in the study chose the normal poll flexion.
Another part of the study involved horses being exposed to a "fear test" whilst being ridden either Rollkur or normally. Each horse suddenly encountered a fear-inducing stimulus: a fan blowing air with plastic strips attached to it; and an umbrella that was opened and closed as the horse approached.
The researchers found that horses tended to have higher heart rates and to react more to the fear-inducing stimulus, when ridden in Rollkur rather than in normal poll flexion.
The researcher concluded: "Horses show higher levels of discomfort when ridden in a coercively obtained Rollkur posture compared to regular poll flexion, and that they will avoid being ridden in Rollkur if given the choice."