Summary Necropsies were performed on 496 horses that had a fatal injury or illness at a California racetrack during the period February 20th 1990 to March 1st 1992. The primary cause of death was categorised by breed, activity at time of injury or illness and organ system affected. Most of the submissions were Thoroughbred horses (432) and Quarter Horses (46). Most of the injuries occurred while racing (42%) and in training sessions (39%); with fewer non‐exercise (12%) and accident (7%) related injuries or illnesses. Musculoskeletal injuries accounted for 83% of the Thoroughbred and 80% of the Quarter Horse submissions. The Thoroughbred horses incurred 306 fractures with 263 in the limbs and 90% of those in the forelimbs. The proximal sesamoid bone(s), third metacarpal bone and humerus were the most common bones fractured in Thoroughbred horses and Quarter Horses. Other major causes of death included respiratory, digestive and multi‐organ system disorders.

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Thirty-six Thoroughbred racehorses that died at California racetracks between October 1993 and July 1994 were evaluated for stress fractures in the caudal portion of the thoracic and lumbosacral regions of the spine and the pelvis. The lumbosacral spine and pelvis were collected, debrided of soft tissues and examined visually for the presence of an incomplete fracture line and focal periosteal proliferation, characteristic of a stress fracture.Sixty-one per cent of specimens had evidence of stress fracture in the caudal portion of the thoracic and lumbosacral regions of the spine and the pelvis. Vertebral lamina stress fractures were found in 50% of specimens and were positively associated with the severity of dorsal spinous process impingement and overall severity of articular process degenerative changes. Pelvic stress fractures affected 28% of specimens and occurred more frequently in older horses. Pelvic stress fractures were positively associated with the severity of lumbar transverse process impingement and several ilia1 articular surface degenerative changes.A high prevalence of vertebral and pelvic stress fractures was noted in this sample of Thoroughbred racehorses that died because of unrelated injuries. Vertebral and pelvic stress fractures need to be considered in the clinical evaluation of horses with back problems or hindlimb lameness. Undiagnosed stress fractures of the vertebrae or pelvis could be a significant cause of poor performance and lameness in Thoroughbred racehorses.