Researchers have recommended routine bit area monitoring from riders and competition organisers having found more than 52% of event horses suffered acute injuries to their mouths during cross-country rounds.
The study, led by Kati Tuomola in Finland, was published in the journal Frontiers in Vet Science on 31 March.
It also found that thinner or thicker than average bits were more likely to cause problems; mares were also more at risk.
The research was conducted on 208 horses at eight events across three locations in western Finland during the summers of 2018 and 2019. The sample size represented 25% of Finnish event horses competing in a given season.
Competitors were invited to volunteer their horses for veterinary inspection following their cross-country rounds, with 95% agreeing to participate.
Of the 52% of horses who had oral lesions, 22% were classed as mild, 26% as moderate and 4% as severe, with the inner lip commisure (the corners of the mouth) found to be the area most vulnerable to damage.
Bruises were found in 39% of all horses and wounds in 19%, although none of these were graded as deep. Typically, only a single lesion was present and only one horse was found with blood inside the mouth.
Bit thickness and type was implicated in injury risk — bar lesions were the second most common site of injury, recorded in 12% of horses and typically found in horses who had unjointed bits.
Horses in thin or thick bits had a higher risk of moderate or severe lesions than those in middle-sized bits, although the researchers noted that double-jointed bits were usually middle-sized while straight-bar bits tended to be thicker.
The researchers concluded that middle-sized bits were probably the best choice for a horse “if the size of the oral cavity was unknown”.
Old/healed lesions were not included in the analysis, but they were also noted in 52% of animals.
“We encourage adopting bit area monitoring as a new routine by horse handlers and as a welfare measure by competition organisers for randomly drawn horses since oral lesions in the bit area were common after a competition even though no external bleeding was observed,” the study’s authors said.
“In riding horses, bit-related lesions can be monitored in competition environment with systematic oral examination by using a headlamp, unlatching nosebands, and possibly curb chains, and lifting the bit while examining the bars of the mandible.”
The research also queried whether “sex-based stereotypes” may be behind the increased number of lesions seen in mares.
“Literature suggests that sex-based stereotypes may compromise mare welfare if their behaviour is interpreted arising from gendered beliefs or if pain-related behaviours are ignored,” the authors said.
The new rule is to be introduced from 1 January 2018 following research linking tight nosebands to mouth lesions
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Horse breeds were also found to be more at risk of lesions than pony breeds.
“For both subgroups, differences in mucosal wound susceptibility or healing capacity cannot yet be ruled out, as wound healing is faster in ponies than in horses and, in humans, oral mucosal wound healing capacity is slower in women than in men,” the authors added.
Previous research on Finnish trotters found that 84% of horses had lesions following a race. A study on event horses in Denmark found the number of lesions to be six times lower but only the outside of the mouth was inspected.
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