Third metacarpal bone length and skeletal asymmetry in the Thoroughbred racehorse.

In man, the dominant right hand is often larger than the nondominant left hand. However, in horses, skeletal asymmetry has not previously been reported. Skeletal asymmetry in the racehorse may influence the way it races and affect the incidence of lameness. The growth in length of the third metacarpal bone (McIII) in the horse has ceased by age 10 weeks (Fretz et al. 1984) and its length should therefore not be affected by subsequent training conditions. Horses are not trained at all until at least age 2 years. This means that measurements of the length of McIII may show any underlying asymmetry in the processes of growth present in racehorses that may affect their performance and the incidence of injury. The aim of this study was to establish whether there was a consistent difference in McIII length in two independent groups of Thoroughbred racehorses.