The basic reason is easy enough to understand, although I struggled to explain this to my girlfriend yesterday at a friend’s Kentucky Derby party. Horses need to stand with their weight distributed evenly in order for their circulatory systems to work properly and avoid infections, and Eight Belles’ two broken ankles apparently means that she would never be able to stand again.

While this Yahoo Answers response kind of explains the necessity of euthanizing broken-legged horses (or at least does so better than this animated Yahoo Answers question and response to a significantly simpler question), the broader question of how it comes to this — and why it does so so often — is significantly more complicated. While these breakdowns may come down to a simple fault of physiology, the Washington Post‘s Sally Jenkins sees a sport with a serious exploitation problem. If you can get past some unfortunately clumsy writing from Jenkins — Eight Belles apparently “ran with the heart of a locomotive;” I have often been described as “drinking with the liver of a helicopter,” but that still seems pretty infelicitous — Jenkins seems pretty right on, at least to me.

[T]horoughbred racing is in a moral crisis, and everyone now knows it. Twice since 2006, magnificent animals have suffered catastrophic injuries on live television in Triple Crown races, and there is no explaining that away. Horses are being over-bred and over-raced, until their bodies cannot support their own ambitions, or those of the humans who race them. Barbaro and Eight Belles merely are the most famous horses who have fatally injured themselves. On Friday, a colt named Chelokee, trained by Barbaro’s trainer Michael Matz, dislocated an ankle during an undercard for the Kentucky Oaks and was given a 50 percent chance of survival. According to several estimates, there are 1.5 career-ending breakdowns for every 1,000 racing starts in the United States. That’s an average of two per day.

…Modern thoroughbreds are bred for extreme speed, maybe to the point of endangerment. Thoroughbreds are muscularly more powerful than ever, but their bone skeletons seem to be getting lighter and frail. A Kentucky Derby horse has to run a mile and a quarter on a dirt track around two turns by the age of 3. It is the horse equivalent of asking a college kid to play in the Super Bowl. A racehorse therefore has to be bred for many things at once: strength, speed, size and stamina, and it has to be fast maturing, as well.

Unsurprisingly, the novelist Jane Smiley’s essay in the New York Times is a good deal better written. While it also covers some of the same turf as Jenkins’ piece, Smiley clearly understands both the sport and the solutions in the works.

It is not racing per se that is cruel, it is American racing as it has been, on dirt tracks at continuous high speeds, for lots of money. Horses in Europe, who run on the turf and only exert themselves all out at the end of fairly long races, do not break down as frequently as American horses on American tracks. American horses bred like European horses, that run in races on the grass, also break down less. American horses have been expected to start racing early and to go fast from the post to the wire, because the people in the grandstands can see the whole race and like plenty of speed.

Fortunately, American racing authorities are finally waking up to the industrywide damage that a high injury rate does, and American racetracks are in the process of changing their racing surfaces from dirt to something called polytrack that is easier on the horses and rather similar to turf. Although horsemen complain because the surface is unfamiliar, a friend of a friend I know at Hollywood Park said recently that her job had changed ” and her job is doing the paperwork on horses injured at the track. She says that she did 75 to 80 percent less paperwork now; that is the difference, for the better, in the injury rate in Southern California since the switch to polytrack. The track at Churchill Downs is still dirt. The difference in the surface means that breeders have to breed a different style of horse, too: sturdier horses with a different action, like European horses.

It is possible, though, that Eight Belles would have run herself to death on any surface. We all know people who cannot admit defeat, and horses can be the same. We all know people who simply defy their own weaknesses and go on. I see Eight Belles™s death as heroic in that sense ” stubborn and foolish, shocking and tragic, but not, in the end, an accident. I think the filly™s courage deserves respect, not pity.