They weren’t born to run.
They were born to graze. They are prey animals. They gallop full pelt to get away from a predator in short bursts rather than endured galloping for a sustained length of time.
Yes, we have bred them to maximise speed and endurance but nonetheless horses were no more born to charge at top speed for a lengthy period than any other prey animal.
Sorry but this isn't true. I think this James May video explains why better than I can.
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- heart bigger than a volleyball
-lungs that laid flat out would cover the size of 10 tennis courts
-ability to pump 75 gallons of blood around their body in under 2 mins
- a spleen which provides a "supercharge" of red blood cells when horse is going at its fastest
But yes, it's great horse welfare to let these majestic beasts just loll around in a field and do nothing. Or let's just let them become extinct which they will do if not raced - look what has happened to heavy horses now they are no longer in work - the Suffolk Punch is rarer than the giant panda.
There is nothing wrong at all with an animals doing what it is bred for and in my own personal experiences, animals, just like humans, are happier when they have a "job" ie a good balance between exercise, stimulation and relaxation and rest.
Btw - have you ever visited any horses who are "born to graze"? Because I have (semi-feral horses in Argentina which are left to graze and breed and only rounded up to be recorded once a year) and they were the most miserable bunch of equines I had seen in a long time. Not all of them, but many were thin from lack of food and high worm burdens, dragging infected or broken limbs, eaten away by flies. Horrid.