An anatomical study of the rostral part of the equine oral cavity with respect to position and size of a snaffle bit

Fluoroscopic study of oral behaviours in response to the presence of a bit and the effects of rein tension

“…This lends support to the suggestion that horses use their tongues to control the distribution of bit pressure within the oral cavity 11,17 . Two lingual behaviours, retracting and bulging of the tongue, which are interpreted as resistances to the action of the bit, increased significantly with rein tension.…”

“…Normally, the tongue covers the interdental space and forms a protective pad between the bit and the gum overlying the edge of the mandible 17 . In the absence of rein tension, only two horses retracted the tongue, whereas this behaviour was recorded in five of the six horses when tension was applied to the reins.…”

A Cross-Sectional Epidemiological Study of Prevalence and Severity of Bit-Induced Oral Trauma in Polo Ponies and Race Horses

“…Manfredi et al (2005) also found that the snaffle bit places pressure upon the tongue under rein tension, causing the horse to retract or bulge the tongue over the bit. This provides relief from bit pressure on the hard palate or provides the tongue relief from bit pressure from itself and distributes some of the pressure onto the interdental space (Engelke & Gasse, 2003;Manfredi et al, 2005). Unlike the snaffle, there is little research into the gag's action on oral structures under rein tension, and so without radiographic evidence, it can only be assumed that the gag does not permit the retraction of the tongue as easily as does the snaffle.…”

“…Lengthening the shanks of the gag increases leverage and severity; however, it also gives the horse increased signaling and faster pressure relief, which may limit oral trauma (G. Bennett, 2001). Engelke and Gasse's (2003) study of cadavers showed that the tongue would take the full force of the bit by splaying upon rein tension to reduce pressure on the bars. Thus, it is suggested that the horses who lean on the bit may increase lingual compression to relieve bit pressure from the bars, resulting in a potential increase in the prevalence of tongue lacerations (Engelke & Gasse, 2003;Manfredi, Clayton, & Rosenstein, 2005).…”

“…Engelke and Gasse's (2003) study of cadavers showed that the tongue would take the full force of the bit by splaying upon rein tension to reduce pressure on the bars. Thus, it is suggested that the horses who lean on the bit may increase lingual compression to relieve bit pressure from the bars, resulting in a potential increase in the prevalence of tongue lacerations (Engelke & Gasse, 2003;Manfredi, Clayton, & Rosenstein, 2005). Acute trauma to the bars resulted in edema and, if severe, bony sequester or exostosis (bone spurs; Johnson & Porter, 2006).…”