Contact and performance problems in horses are frequently attributed to the type of bit used, and there has been much research into horse interaction with the bit. Interaction between the horse and other parts of the bridle appear to have been neglected even though problems are often not resolved by alterations in bitting alone.
Traditional bridle design positions the parts of the bridle over various anatomic prominences and moving parts of the head, it is therefore important to understand interactions between parts of the bridle and the horse's head. Excessive noseband pressure in horses has been raised as an issue potentially effecting welfare, performance, and injury, particularly with respect to use of crank nosebands with double bridles. However there has been minimal scientific investigation performed. Various headpiece designs have been marketed that claim to reduce pressure around the headpiece and to improve performance as a result. However there appears to be little scientific research behind these claims.
The objectives of this study were three fold:
1. To determine the sites of maximum pressure under the headpiece of a double bridle, and under a standard crank cavesson noseband in trot using a pressure mat recordings;
2. To design a double bridle headpiece and crank cavesson noseband combination that avoids sites of maximal pressure during movement; and
3. Compare the two bridles with regard to maximum pressure and equine gait kinematics (gait quality)
Two small format pressure mats with multiple sensors were positioned on the horse's head, one underneath the headpiece and one over the horse's nasal bone underneath a cavesson crank noseband with the bridle fitted normally to the horse. Magnitude of peak pressure at each sensor on the pressure pad was recorded.
For all headpieces in all horses, high peak pressures were consistently located near the distal ends of the headpiece on either side at the base of the ears. Interestingly additional locations of high peak pressures varied between headpiece designs.
For wide headpieces (6cm wide), there were high pressures on the caudal margin (back) of the headpiece at the area of impact with the wings of the atlas on either side.
Where the noseband strap was positioned underneath the headpiece, there were increased pressures on the midline over the top of the head with the highest pressures recorded in rolled bridles, where the rolled noseband and bridoon lay on top of one another inducing focal pressures.
When the headpiece of the noseband was the full width of the headpiece, attaching underneath and crossing the top of the head as one unit, there appeared to be greater cranial and caudal movement of the bridle, creating high peak pressures at the front of the head piece (i.e. at the back of the ears), and the back of the headpiece against the wings of the atlas (the first bone of the horse neck, the first cervical vertebrae) See Figure 1.
In addition, there were frequent but intermittent high pressures recorded under the headpiece close to the junction with the brow band, which were still present when the brow band was removed and did not appear to be influenced by the rider. It was thought that this intermittent pressure may be associated with movement of the tongue with swallowing actively creating pressures against the bridle.
The location of maximum pressure under the headpiece in a standard bridle was located immediately ventral to the base of the ear, overlying the parotid salivary gland superficially; various branches of the facial nerve (including to the ear) and external acoustic meatus more deeply. This region includes areas of muscle attachment for the flexors of the skull (muscles responsible holding the head in a vertical position. It is therefore understandable that relief of pressure at this location might lead to improved submission and movement. As the head and neck are important for balance in the horse, increasing freedom to use different muscle patterns to achieve a training position might improve balance and therefore ability to alter gait. If the bridle design changes the pressure and force distribution on the head, then the change in peak pressure may allow the muscles in that area to work more effectively as they are not having to work against the pressure that was previously placed on them. Peak pressures of >4.67 kPa have been suggested as a cause of damage, based on lack of tissue perfusion, and pressures >30 kPa under a saddle have been associated with back pain. The magnitudes of peak pressure and maximum force recorded under the headpiece and noseband of horses in this study were considerably higher than these figures. This could explain potential discomfort, and results of one study did suggest that tight nosebands could be restricting cutaneous blood flow. However, it has also been suggested that intermittent relief of pressure reduces tissue damage, and the pressures observed under the noseband and headpiece were largely intermittent. No evidence of tissue damage or white hairs were detected under the noseband or headpiece on the horses evaluated, supporting a lack of significant skin damage.
For all nosebands peak pressures were consistently located either side of the nasal bone. The position of the horse's head appeared to influence the location of pressure on the noseband. It is possible, therefore, that movement or positioning of a horse's head could be influenced by the horse seeking relief from noseband pressure.
Bridle Design for Reduced Peak Pressure
Based on the results of Part 1, a bridle was designed to avoid the locations of peak pressure (Bridle F). Cushioned pads were fitted near the distal ends of the headpiece to ensure clearance was maintained at the base of and ventral to the ear where pressure peaks were recorded. A large central lozenge was incorporated in the headpiece to maintain stability, and the sides of the headpiece were narrowed to avoid interference with the wings of the atlas and the caudal margin of the ears. The position of the billet split was lowered to increase stability, and the noseband was attached to both sides of the headpiece independently to avoid high pressures over the midline of the headpiece. The headpiece of the bridle was lined with a pressure absorbing material to improve the interface with the horse's head and nose. (Prolite, Fairfax saddles, Walsall, UK).
The noseband was fitted with two large rings and two smaller rings to enable the noseband to articulate and move with the horse's head rather than antagonistically. A cushioned pad was fitted in the center of the noseband to maintain clearance of either side of the nasal bone where peak pressures were recorded. The entire noseband was also lined with a high performance pressure absorbing material.
Effect of Bridle Type on Pressure Distribution and Gait Parameters
Pressure patterns under the headpiece and the noseband were compared between Bridle F, and the horse's usual bridle, Bridle S. Gait quality was also assessed.
Significantly lower maximum force and significantly lower peak pressure were detected under the headpiece and noseband with Bridle F compared to Bridle S. Peak pressure under the browband was 106.7% greater in Bridle S compared to Bridle F, and maximum force was (mean) 59.7% greater with Bridle S than Bridle F.
Horses wearing a bridle designed to avoid locations of maximum pressure exhibited a greater degree of carpal (knee) and tarsal (hock) flexion and a greater degree of forelimb protraction was seen. Thus the bridle was associated with improved expressiveness of the trot.
All riders reported a difference in work quality between bridles, reporting a positive effect of Bridle F. A marked difference was reported by 9 of 12 riders for straightness,for rhythm, suppleness, and impulsion, as well improved scores for contact and collection.
In summary, using a bridle designed to avoid locations of maximum pressure led to lower maximum pressure under the noseband and headpiece compared with the horse's usual bridle and was associated with improved gait quality at the trot, including greater carpal and tarsal flexion, compared with the horse's usual bridle.