In the wild they would not be limited to the area they can roam and would be able to acces natural mineral deposits the same as deer, elk, moose and other wildlife. There is also a big difference in quality of life between wild horses and domestic horses.

What Gunsling said. Additionally, many areas where wild horses roam have areas where the soil or rock has a high salt contact. Herbivorous animals will go to these areas for the salt content. (Hunters like to stake out these areas.)

Also, some plants concentrate salt in their tissues, and grazing animals will seek these plants out.

Wild horses are rarely asked for the kind of physical performance we expect of our high-performance sport, race or show horses. They are also rarely in top physical condition, although they can be quite tough. And when the available food sources are inadequate in any required nutrients, they die.

They have licking rocks and natural parasite control

ok Karen you were only partly right the mustang would out do any horse that is domesticated, I can see you have never seen what a mustang is capable of, they are one of the smartest animals.

I have seen 3 mustang herds threw 35 years and another herd for 5 years if you have ever seen where they live and the different types of areas that they and if they ever do die out it will because of a human not because of where they live

All animals need salt. The grazers could smell salt and mineral deposits with a high salt content.
There are well established 'salt licks'
all over this country that were/are used generationally. The Indians knew of and used them as well as the herds of horses, bison, elk, antelope and deer and dozens of other kinds of animals.

"A salt lick is a salt deposit that animals regularly lick. In an ecosystem, salt/mineral licks sometimes occur naturally, providing the sodium, calcium, iron, phosphorus and zinc required in the springtime for bone, muscle and other growth in deer and other wildlife, such as moose, elephants, cattle, woodchucks, domestic sheep, fox squirrels, mountain goats and porcupines. Harsh weather exposes salty mineral deposits that draw animals from miles away for a taste of needed nutrients." WIKI