Radiographic study of bit position within the horse's oral cavity

The objective was to describe and compare the positions of different types of bits within the horse’s oral cavity. Eight horses were fitted with a bridle and six bits [jointed snaffle ( JS), Boucher, KK Ultra, Myler snaffle (MylerS), Myler ported barrel (MylerPB), Myler correctional-ported barrel (MylerCPB)]. Lateral radiographs and custom software were used to measure the position and orientation of the bits relative to the horse’s palate and second premolar teeth without rein tension and with 25 ^ 5 N bilateral rein tension. The results showed differences in the position of the bits within the horse’s oral cavity and in their movements in response to rein tension. Without rein tension, single-jointed bits were further from the premolar teeth ( JS 32.2 ^ 10.6 mm; Boucher 33.9 ^ 10.8 mm) than the Myler bits (MylerS 20.2 ^ 9.7 mm; MylerPB 12.8 ^ 6.7 mm; MylerCPB 14.6 ^ 4.3 mm). Single-jointed bits moved closer to the premolars when tension was applied to the reins (JS 20.8 ^ 6.3 mm; Boucher 19.7 ^ 6.8 mm). The cannons of the Boucher were more elevated than those of the other bits. The cannon angulation decreased significantly from 38.7 ^ 13.7 deg. to 21.6 ^ 6.9 deg. for JS and from 43.1 ^ 10.1 deg. to 27.8 ^ 10.1 deg. for the Boucher when tension was applied to the reins. The Myler bits showed minimal change in position in response to the application of rein tension.