Does a broken leg Always mean that a horse needs to be put down? Or can some broken legs heal in horses?
It depends on the type and location of the fracture. Something like a hairline fracture has a decent prognosis but something like a comminuted fracture typically has a bad outcome.
Vets have made amazing advancements in the treatments of orthopaedic injuries in horses; unfortunately, the outcome of an injury is not just dependent on the care the animal is given but also is dependent on the personality of the animal.
A horse can receive a fairly minor fracture but, due to panicking, can turn it into an incredibly complicated one. Unfortunately, a horse doesn't understand that they mustn't use a limb that's been broken - I've seen a video of a horse that had a compound fracture (feral mustang, jumped out a corral and caught its leg on the fence, I could probably dig up the video if anyone wants to see it) and the horse kept running on it.
Fractures can result in a horse being required to be on stall rest for months, some fractures even require a horse to be placed in a sling (horses cannot lie down for more than a few hours without dying.)
Horses don't tend to do very well when being confined like this and their agitation can result in them worsening their injury. A lot of horses are also athletes who are used to getting a decent amount of regular exercise - to then be confined to a small space for months can be horrible for them. Confinement and being unable to put much weight on one leg can also cause the horse's other legs to develop laminitis (which can be bad enough in and of itself to need a horse to be euthanised.)
