Bit-related oral lesions are a common and painful welfare issue in horses. Even though horses have been ridden and driven with a bit and bridle for 6000 years and bit sores have been described already in the 19th century in the veterinary literature, scientific reports on bit-related lesions and their risk factors in horses remain scarce.
The aim of this thesis was to (i) determine the occurrence of oral lesions in the bit area in Finnish trotters and event horses after competitions, (ii) create a scoring system for oral lesions in the bit area and demonstrate different lesion types and locations with photographs, (iii) investigate risk factors for bit-related lesions in trotters and event horses, (iv) further investigate different stakeholders’ attitudes towards bit-related lesions in trotters.
The rostral part of the mouth of 469 horses (261 trotters, 208 event horses) was examined systematically after a competition. Trotters were examined in 10 racing events in 2017 and event horses in 8 competition events in 2018–2019. Many horses had multiple lesions, and therefore, a lesion scoring system was created in which points were given to each lesion depending on its size, type (bruise or wound), and depth (superficial or deep). Points for each lesion were summed such that each horse received a total lesion score that reflected the overall lesion status. No acute lesions were found in 42 trotters (16%), and lesion status was mild in 55 trotters (21%), moderate in 113 trotters (43%), and severe in 51 trotters (20%). In event horses, no lesions were found in 99 horses (48%), and lesion status was mild in 45 (22%), moderate in 55 (26%), and severe in 9 horses (4%).
The most common lesion location was the inner lip commissure. Lesions were also found in the bars of the mandible in front of the first lower cheek tooth, in the buccal area near the first upper cheek tooth, and in the outer lip commissures. Only a few horses had mild lesions involving the tongue and one horse in the hard palate. Although 109 event horses and 219 trotters had oral lesions in the bit area, none of the event horses and only six trotters showed external mouth bleeding. Additionally, one event horse and 26 trotters had blood inside the mouth or on the bit when it was removed from the mouth.
Associations between a horse’s moderate-severe oral lesion status and potential risk factors were analyzed with multivariable logistic regression analysis. The association between bit type and lesion location was examined with Fisher’s exact test. Risk factors for moderate-severe oral lesion status in trotters were the use of a Crescendo bit, a mullen mouth regulator bit, or an unjointed plastic bit (model Happy Mouth) and female sex (mare). In event horses, the risk factors were thin (10–13 mm) and thick (18–22 mm) bits, female sex (mare), and other than pony breed. In both disciplines, unjointed bits were associated with lesions in the bars of the mandible. Single-jointed snaffle bits were the most common bit type in trotters and the least associated with moderate-severe lesions. In event horses, double-jointed 14–17 mm bits were most common. Bit thickness of 14–17 mm was the least associated with moderate-severe lesion status. However, these results may at least partly reflect driveability or rideability issues, and thus, rein tension differences because drivers/riders may change to distinctive bit designs if they have difficulty eliciting an appropriate response with rein cues.
In the pilot questionnaire study, imaginary scenarios and photographs of lesions from horses’ mouths were presented to different stakeholders (veterinarians and race veterinary assistants, trainers, and others). They were asked in multiple choice questionnaires whether they allow the horse to start in the race, stipulate a health certificate before the next race, or remove the horse from the race. The association between stakeholder groups and their answers was examined with the Pearson Chi-square test. The results of this study indicated differences in attitudes towards bit-related lesions between stakeholder groups but also within a stakeholder group. This might reflect differences in conflicts of interests, moral values, empathy, or over-exposure to oral lesions. Not removing horses with severe oral lesions from the race may compromise horse welfare and society’s trust in the surveillance system.
In this study, oral lesions in the bit area were common after a competition, although only few horses showed external bleeding. Oral examination and an oral lesion scoring system with an assistant recording the findings were suitable for field conditions and horses seemed to tolerate the examination well. Even though changing the bit to the bits least associated with lesions may be beneficial, horses with oral lesions might benefit from training modifications. Given the higher risk observed for mares in this study, mare oral health warrants special attention. Results of this thesis encourage adopting bit area monitoring as a new routine by horse handlers and as a welfare measure by competition organizers in order to minimize pain and negative experiences by early diagnosis and treatment of mouth lesions.