A comment on bit-related lesions in Icelandic horses. Jens Tolboll Mortensen, as a private person 8 December 2014 In Acta Veterinaria Scandinavica 2014, 56:40 Björnsdottir et al presented an investigation on Icelandic horses, in which they concluded that bit related lesions in the mouth was a general problem in competition horses and that the use of a particular bit, curb bit with a port, was a decisive risk factor for lesions on the bars of the mandible. The study included repeated examinations of the horses reaching the finals. There were no records on the bit used during the training before the competition and no information on the horses temper (will and spirit). The effect of the rider was not included in the analysis. The results showed more lesions in the bar region after the second examination and a correlation between the use of a snaffle bit and lesions in the buccal region and between the use of a curb bit with port and lesions in the bar region. Confounding by indication, the phenomenon in my medical world where treatments tend to look harmful just because they are only given to sick people, may explain these results. Meaning in this respect, that the curb bit with port might be used more often with horses that are difficult to ride and therefore are at a higher risk of developing lesions, maybe irrespective of the bit used. Another way of saying this is that the indication for treatment may be related to the risk of future health outcomes. Given the conclusions in this study, I think it would have been interesting to include the temper of the horse, the bit used during training and the rider in the analysis before announcing a causal relationship to a specific bit. Yours sincerely, Jens Tølbøll Mortensen, MD, PhD, Kollerup Strandvej 11, DK-9690 Fjerritslev, Denmark. E-mail: email@example.com. Competing interests None.