Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings.

REASONS FOR PERFORMING STUDY: To improve the understanding of exercise related sudden death in Thoroughbred racehorses.
OBJECTIVES: To describe the post mortem findings in cases of sudden death associated with exercise in 268 Thoroughbred racehorses.
METHODS: Gross and histological post mortem findings of 268 cases of sudden death were collated and reviewed. Cases originated from 6 racing jurisdictions around the world. Sudden death was defined as acute collapse and death in a closely observed and previously apparently healthy Thoroughbred racehorse, during, or within one hour after, exercise. Cause of death as determined by the attending pathologist was categorised as definitive, presumptive or unexplained and compared between the different populations. Cardiopulmonary lesions recorded at post mortem examination were compared between different populations.
RESULTS: Pathologists recorded a definitive cause of death in 53% (143/268) of cases. Major definitive causes of sudden death included cardiac failure, apparent pulmonary failure, pulmonary haemorrhage, haemorrhage associated with pelvic fractures or with idiopathic blood vessel rupture, and spinal cord injury. A presumptive cause of death was made in 25% (67/268) of cases and death remained unexplained in 22% (58/268) of cases. There were several statistically significant inter-population differences in the cause of death and in reporting of cardiopulmonary lesions.
CONCLUSIONS: Sudden death can be attributed to a variety of causes. Causes of sudden death and the lesions found in cases of exercise-related sudden death are similar in different racing jurisdictions. However, the lesions are often not specific for the cause of death and determination of the cause of death is therefore affected by interpretation by the individual pathologist.