Objective—To use quantitative ultrasonography to evaluate the association between the speed of sound (SOS) at 9 sites in the third metacarpal bone (MCIII) of racing Thoroughbreds with workload accumulation and the effect that MCIII failure has on this association.
Animals—Sixty-two 2- and 3-year-old Thoroughbreds in racing condition.
Procedures—Cumulative work index (CWI) was used to calculate total workload (CWItotal) and also 3 independent CWIs for the various gaits (ie, trot [CWItrot], gallop [CWIgallop], and race [CWIrace]) used during training and racing. Speed of sound was monitored in horses during the 2007 racing season and compared with the CWIs via regression analysis. Sex, age, limb, and MCIII failure were included as covariates in the model.
Results—SOS was significantly associated with CWItotal at 8 sites and with independent CWIs of the various gaits at all 9 sites. Progression of SOS in MCIIIs with workload differed significantly in horses with clinical signs of metacarpal bone failure, compared with results for horses with clinically normal MCIIIs, in 1 site by use of CWItotal and in 5 sites by use of the independent CWIs for the various gaits.
Conclusions and Clinical Relevance—These results indicated that SOS in the MCIII of racing Thoroughbreds followed a constant pattern of progression as workload accumulated. With the development of more precise quantitative ultrasonography devices, SOS corrected for amount of activity may be used to identify horses at risk of bone failure.