Not an answer as such, but as I run a herd of natives in a semi-wild state, I can offer some observations:
'wild' pasture is not fertilised or sprayed.
'wild' ponies don't receive hard feed or concentrates (even a bit of molassed chaff is much richer than rough pasture)
'wild' horses are constantly on the mooch looking for food, which stimulates their circulation, especially in the legs / feet.
'wild' pasture isn't just grass, it's all sorts of weeds and such which offer nutritional goodies, and indeed toxins, allowing horsey to self-medicate. (thistles are popular when the grass is lush)
Unshod horses hooves expand/contract as they move around, which acts as a circulation pump.
I think they're also less bored, able to express themselves more naturally, so less food-fixated.