A horse is a gentle, thoughtful creature that is prone to flight if the rider isn’t calm assertive and in control.

The reason is simple, they are heard animals and they have a very strong flight instinct if the heard so decides.

I’m sorry but most of the explanations on here or partially or completely wrong. I am a vet student focused on equine medicine and was just recently discussing this with one of my professors who is a renowned equine surgeon and has cut open more horses than most people have ever seen.

There are several reasons:

  • Horses are pretty weird anatomically – they have no muscles below the knee. Part of their ability to run super fast is this really incredible tendon/ligament system – muscles higher on the body load the tendons and ligaments with huge amounts of power (picture a spring). Because of this, the bones in their lower leg (which is almost always where they break) are relatively very thin but also generating massive power. This ratio is much more extreme in the horse than other animals, so it means that solving it with a few pins like you might in other animals won’t do the trick. In addition, this massive power makes it more likely that the horse will basically shatter the bone rather than just a simple break or fracture . Also, they’re just really big.
  • If the horse can’t move his legs around, he can’t circulate blood through properly and it somewhat pools in the hoof and the attachments of the hoof to the bottom of the leg weaken. Compare this to a human or dog, where we can wiggle our toes and whatnot to help move circulation through – remember, horses have no muscles below the knee.
  • Trying to keep a horse from moving around for any extended period of time is a nightmare. There’s a saying I heard that all horses have two goals in life: homicide and suicide. They will colic and die if a bird looks at them wrong. In addition to the possibility of foundering, a horse is pretty likely to just lose his marbles if you try to keep them sedentary for too long – they may try to climb out of their stall, break whatever apparatus they’re in, colic (severe and sometimes fatal stomach ache), get ulcers and whatever else. You can’t force them to lay on their side for very long at all – they’re too heavy and will have difficulty breathing and damage nerves.

When deciding whether or not to save an animal, quality of life must always be considered. A dog may do perfectly well and have a wonderful life in a cast for a while and then with a moderate limp – this is not true for horses. Further, cost can be very prohibitive; it’s worth it for very very expensive horses (think Barbaro) but for your average pleasure horse, the cost and pain is just not worth it or generally feasible.