Bit-related lesions in competition horses have been documented, but little evidence exists concerning their potential risk factors.

To explore potential risk factors for oral lesions in Finnish trotters.

Cross-sectional study.

The rostral part of the mouth of 261 horses (151 Standardbreds, 78 Finnhorses and 32 ponies) was examined after a harness race. Information on bit type, equipment and race performance was collected.

A multivariable logistic regression model of Standardbreds and Finnhorses showed a higher risk of moderate or severe oral lesion status associated with horses wearing a Crescendo bit (n = 38, OR 3.6, CI 1.4–8.9), a mullen mouth regulator bit (n = 25, OR 9.9, CI 2.2-45) or a straight plastic bit (n = 14, OR 13.7, CI 1.75-110) compared with horses wearing a snaffle trotting bit (n = 98, P = .002). Bar lesions (67 horses) were more common in horses wearing unjointed bits than in horses wearing jointed bits (Fisher's exact test P < .001). Lesions in the buccal area and the inner lip commissures were not associated with bit type. Using a tongue-tie or an overcheck, galloping, placement in the top three or money earned in the race were not associated with lesion risk.

The sample size for certain bit types was insufficient for statistical analysis.

Moderate and severe oral lesion status was more common in horses wearing a Crescendo bit, a mullen mouth regulator bit or a straight plastic bit than in horses wearing a single-jointed snaffle trotting bit. However, lesions were observed regardless of bit type. Further studies on rein tension, the interaction between bit type and rein tension and prevention of mouth lesions in trotters are warranted.