Hereditary Multiple Exostoses-A Comprehensive Examination of a 4-Year-Old Dutch Warmblood Male With Maternal Links to HME in First and Second Generations

Hereditary multiple exostoses (HME) is a condition rarely diagnosed in horses, which has not been previously reported in Dutch Warmblood horses. Its presentation resembles that diagnosed in humans, and it is predominantly active during periods of skeletal maturation. This case study reports a link between a granddam with no obvious HME lesions and its first and second generations presenting with HME, albeit with different sires. The severity in affected horses (n = 5) varied from one foreleg to the other with extensive multiple lesions of 123 of 205 bones in a half sibling in the first generation. In the second generation, axial deviations were reported, including similar lesions to those found in the first generation. Rib and limb lesions were the most commonly reported in the first and second generations by age four. However, an extensive examination of the 4-year Dutch Warmblood first generation male revealed lesions from the first cervical vertebra to the first caudal vertebra, inclusive of rib and limb lesions. As all horses with this condition are untreatable, early detection and diagnosis would provide the owner/breeder with options to avoid financial loss and emotional stress.