A Photographic Methodology for Analyzing Bit Position Under Rein Tension

Bits are a common and invasive piece of equipment used in equestrian sports. A bit should be carefully chosen to suit the individual horse according to the pressure points it is willing to accept. Bit pressure is poorly understood due to a lack of accessible research instruments. The objective of this study was to describe a method to estimate pressure points from the bit on the tongue without the need for radiographs. The method uses photographic images of horses under static rein tension. Using design features on the bit, the angle at which these features press into the tongue were calculated. Ten riding school horses wearing a snaffle bridle without a noseband, were used to measure the degree to which a bit rotates under 2 kg of static rein tension for a Turtle Top snaffle bit, French Link snaffle bit, Herm Sprenger single-jointed snaffle bit, and ported Weymouth bit. Six dressage and eventing horses were used to measure the effect of rein tension, in 0.5 kg increments, on the degree of rotation of the bit. The bit rotated, but not significantly (P > .008), over the rein tensions used (up to 2 kg). The reliability of the proposed method was confirmed by comparing anatomical reference lines in photographs with those in radiographs. The findings provide a reliable estimate to determine pressure points from a bit on the tongue, under rein tension without the need for invasive techniques and in the absence of technologically adequate equipment.