Exhaustion Point

Question
Hi,
 I am currently reading a book set in the 1850s and there is a part a in there
about horses I  would like to ask about. In the book there is a point where a
young man is riding his horse just for fun out in the fields and really running
him, not too much but enough so the horse is really tired.Just when he is about
to stable his horse he finds out his dad is dying and needs the doctor asap. So
he gets right back on and rides the nearly 5 miles into town as fast as his
horse can take him. He gets there and notifies the doc who goes out and manages
to save his dad just in time. Then sadly the boys horse dies of exhaustion.
Is that a feasible scenario as far as that distance along with the already worn
out state of the horse being able to cause death? If not, could you tell me the
distance a horse could go at an all out run before it hurt them? I understand
many factors would be at play such as condition of horse, weight of rider,
temperature, terrain, etc.., I am just talking about a general distance.
Thank You

Answer
Hi Jason -

I don't know how much help I'll be on this but the scenario you describe reading sounds totally feasible to me.  As far as your final question about a general distance ... I couldn't begin to guess.  There are countless variables as you mentioned but on top of that, horses are truly amazing and will pull off some unbelievable physical feats for the people in their lives if the bond is a special one.