Bit-Related Injuries in Harness Racehorses

Selecting and fitting a bit to an individual horse and then using it skillfully and sympathetically serve as hallmarks of nuanced horsemanship, no matter the discipline. When mouth injuries directly related to bitting occur, even the most conscientious of horsemen are often baffled by their appearance. Researchers attempted to pinpoint the root cause of these injuries in a recent study of harness racehorses.^* Should the blame be assigned to specific bits, other pieces of common equipment, or race performance?

Researchers examined the mouths of 261 trotters, including 151 Standardbreds, 78 Finnhorses (a native lightweight draft), and 32 ponies, for bruises and wounds immediately following a race. They looked at specific bit-contact areas: the inner and outer corners of the lips, bars of the lower jaw, cheek tissue near the second premolar tooth, tongue, and roof of the mouth.

The researchers then collected information about the type of bit used for each horse, making special note of the thickness and composition of the mouthpiece. Details of other equipment were taken, when applicable, including the use of an overcheck, jaw strap, or tongue-tie. Past racing history was mined from a reliable online database.

Injuries were observed in 84% of the horses in the study, regardless of the type of bit worn, and half of those were classified as moderate or severe. Five horses (2%) had visual blood outside of the mouth from the wounds.

Compared with horses wearing a single-jointed, half-cheek snaffle, trotters that wore a Crescendo bit, Mullen-mouth regulator bit, or a straight plastic bit had a greater likelihood of moderate or severe injury to the mouth. Bar lesions were more common in horses outfitted with unjointed bits. Other tack and race performance did not factor into risk for oral lesions, according to the researchers.

“While this study serves to highlight the physical injuries caused by bits among specific high-performance horses, it is important to note that lesions may be severe enough to hinder comfortable chewing of forages, especially if hay or chaff is stemmy,” said Catherine Whitehouse, a nutritionist with Kentucky Equine Research. This in turn could affect forage consumption, leading to diminished body condition, onset of gastric ulcers, and loss of performance.

Further, mouth pain can be a source of worry or stress for horses, even while resting. “Racehorses have a high incidence of gastric ulceration, the effects of which can be assuaged by conscientious management, which may include the use of research-proven digestive supplements,” Whitehouse said.

^*Tuomola, K., N. Mäki-Kihniä, A. Valros, and A. Mykkänen. 2021. Risk factors for bit-related lesions in Finnish trotting horses. Equine Veterinary Journal 53:1132-1140.