BY HILARY M. CLAYTON, BVMS, PHD, MRCVS PHOTOGRAPHS COURTESY OF THE MCPHAIL EQUINE PERFORMANCE CENTER V
THE USE OF A BIT IS MANDATORY in dressage competition, and every rider is faced with the challenge of selecting an appropriate bit for his or her horse. Because the bit contacts sensitive structures within the horse’s oral cavity, improper selection, fitting, or use of a bit is likely to cause resistance to the action of the rein or even injury to the horse’s mouth. Areas where the bit crosses a bony surface, such as the hard palate and the bars of the mouth, are particularly vulnerable to painful pressure from the bit.
Tack stores carry a wide range of bits—some familiar, others novel and different (and not all legal for use in recognized dressage competition). In recent years, bits have been designed with the intention of making the horse more comfortable, rather than as a means of increasing the rider’s control, which is certainly a positive step. Unfortunately, there is limited information to help riders choose appropriate bits for their mounts. In an effort to introduce some science into the art of bitting and bit selection, researchers in the McPhail Center have recently completed a series of studies of equine oral conformation and bitting.
In this article, I’ll describe the position of various bits in the horse’s mouth and their relationships to the sensitive structures. A future article will explore the movements of the bit within the oral cavity.
Oral Anatomy
Within the horse’s oral cavity, the bit rests on the tongue and the gums overlying the bars of the mandibles. The hard palate, which forms the roof of the mouth, bounds the oral cavity above. The tongue normally fills the oral cavity, and the bit is interposed between the soft, muscular tongue and the bony, hard palate. When the horse accepts the bit, the muscles of the tongue relax, allowing it to be indented by the bit, thereby relieving bit pressure against the palate.
Oral Conformation
Horses differ in the sizes and shapes of their oral cavities, and these differences dictate the mouthpiece types and sizes that can be accommodated comfortably. Factors to consider include the position of the corners of the lips relative to the bars, the width across the jaw between the corners of the lips on the left and right sides, the shape of the palate (flat or arched), and the thickness and width of the tongue. The first part of our study used xrays to measure some internal dimensions of the horse’s oral cavity. The goal was to determine whether mouth size was proportional to horse size. The subjects were four warmbloods and four Thoroughbreds. The height and length of each horse’s oral cavity were measured radiographically, and these dimensions were correlated with the horse’s height at the withers. The results showed no relationship between a horse’s height and the size of his oral cavity. In practical terms, this finding indicates that we cannot assume that a large horse should wear a bigger bit than a smaller horse.
A Study of Bit Position
Bits vary in size, shape, and mechanics of action. Most riders are aware that individual horses respond better to certain bits, and that these preferences may be related to differences in oral conformation or to the horse’s sensitivity to the mechanism of action. Our subjective judgment of the horse’s response is the main criterion used to select an appropriate bit for an individual horse. The goals of our second study were to describe the position of different types of bits inside the horse’s mouth and to measure their proximity to the horse’s hard palate and premolar teeth, both of which are readily identified on radiographs. The eight horses from the previous study were fitted with a snaffle bridle that was adjusted to produce two small wrinkles at the corners of the lips.
28 DECEMBER 2005 | USDF CONNECTION Bitting: The Inside Story Study examines bit action and its effects on the horse’s mouth
BY HILARY M. CLAYTON, BVMS, PHD, MRCVS PHOTOGRAPHS COURTESY OF THE MCPHAIL EQUINE PERFORMANCE CENTER
THE USE OF A BIT IS MANDATORY in dressage competition, and every rider is faced with the challenge of selecting an appropriate bit for his or her horse. Because the bit contacts sensitive structures within the horse’s oral cavity, improper selection, fitting, or use of a bit is likely to cause resistance to the action of the rein or even injury to the horse’s mouth. Areas where the bit crosses a bony surface, such as the hard palate and the bars of the mouth, are particularly vulnerable to painful pressure from the bit.
Tack stores carry a wide range of bits—some familiar, others novel and different (and not all legal for use in recognized dressage competition). In recent years, bits have been designed with the intention of making the horse more comfortable, rather than as a means of increasing the rider’s control, which is certainly a positive step. Unfortunately, there is limited information to help riders choose appropriate bits for their mounts. In an effort to introduce some science into the art of bitting and bit selection, researchers in the McPhail Center have recently completed a series of studies of equine oral conformation and bitting.
In this article, I’ll describe the position of various bits in the horse’s mouth and their relationships to the sensitive structures. A future article will explore the movements of the bit within the oral cavity.
Oral Anatomy
Within the horse’s oral cavity, the bit rests on the tongue and the gums overlying the bars of the mandibles. The hard palate, which forms the roof of the mouth, bounds the oral cavity above. The tongue normally fills the oral cavity, and the bit is interposed between the soft, muscular tongue and the bony, hard palate. When the horse accepts the bit, the muscles of the tongue relax, allowing it to be indented by the bit, thereby relieving bit pressure against the palate.
Oral Conformation
Horses differ in the sizes and shapes of their oral cavities, and these differences dictate the mouthpiece types and sizes that can be accommodated comfortably. Factors to consider include the position of the corners of the lips relative to the bars, the width across the jaw between the corners of the lips on the left and right sides, the shape of the palate (flat or arched), and the thickness and width of the tongue. The first part of our study used xrays to measure some internal dimensions of the horse’s oral cavity. The goal was to determine whether mouth size was proportional to horse size. The subjects were four warmbloods and four Thoroughbreds. The height and length of each horse’s oral cavity were measured radiographically, and these dimensions were correlated with the horse’s height at the withers. The results showed no relationship between a horse’s height and the size of his oral cavity. In practical terms, this finding indicates that we cannot assume that a large horse should wear a bigger bit than a smaller horse.
A Study of Bit Position
Bits vary in size, shape, and mechanics of action. Most riders are aware that individual horses respond better to certain bits, and that these preferences may be related to differences in oral conformation or to the horse’s sensitivity to the mechanism of action. Our subjective judgment of the horse’s response is the main criterion used to select an appropriate bit for an individual horse. The goals of our second study were to describe the position of different types of bits inside the horse’s mouth and to measure their proximity to the horse’s hard palate and premolar teeth, both of which are readily identified on radiographs. The eight horses from the previous study were fitted with a snaffle bridle that was adjusted to produce two small wrinkles at the corners of the lips.
28 DECEMBER 2005 | USDF CONNECTION Bitting: The Inside Story Study examines bit action and its effects on the horse’s mouth
BY HILARY M. CLAYTON, BVMS, PHD, MRCVS PHOTOGRAPHS COURTESY OF THE MCPHAIL EQUINE PERFORMANCE CENTER