Why can injuries be life-threatening in racehorses?
The most serious type of injury sustained by racehorses are bone fractures. With advances in veterinary medicine a number of fractures sustained by horses can now be repaired, often allowing the horse to continue with either its racing career or another career, however, there are difficulties in repairing certain fractures that are not comparable to humans.
One of the biggest challenges for veterinary surgeons when treating all breeds of horses is not repairing the fracture per se, but the post-surgical complications and rehabilitation of a 500kg animal. Recuperation of a horse is a major welfare challenge, as horses do not adapt well to sustained periods of inactivity during convalescence. Additionally horses are not functionally adapted to or capable of spending large periods of time ‘lying down’ or having a limb put in a sling to prevent weight-bearing and consequently numerous life-threatening complications can result. Complicated, unstable fractures cannot withstand immediate weight-bearing and this means many fractures cannot be repaired. In such circumstances, the most humane measure is to put the horse down.
Additionally the risk of infection after injury, where the skin has been broken, is very high in horses partly due to their physiology and partly due to environmental contamination. Soft tissue injury that accompanies bone fractures in horses can further complicate repair after injury.
An article in The Guardian discussed in more detail the reasons horses have to be euthanased after sustaining certain injuries regardless of how much their owners and carers wish to save them.