If we take a horse & give her sufficient time on each surface, what changes would her hooves make on each?
Of course there are other factors such as diet & exercise, and what state those hooves were in when you put them in a certain environment. But generally, horses on hard surfaces will wear their walls to at/near level with the sole on the ground surface, while horses in soft environments can(should?) manage with longer walls. Horses on hard, flat ground tend to have more 'filled in' feet to horses that are on rough/yielding surfaces. Bare horses with longer walls will chip, split, break off wall(which if designed to be loaded shouldn't happen), whereas short walled, mustang rolled hooves tend to cope fine on this footing. Flat pavement is not generally a problem for horses that aren't peripherally loaded either.
Lee says that the Arabians (lots of sand) have deeply cupped hooves, whereas tb's have flat ones, due to being on soft pasture, & horses who've been on really marshy ground get really big flat feet.
Yep, that's the case alright. As TBs have an awful lot of arab blood & came out of that breed, I don't know that that's the best eg of genetic differences, but yes, different breeds do tend to have slightly different hoof form - like I said, not at all dismissing the genetic argument outright, just don't feel it's a big factor - but how much is it about the environment?
What does it mean that you can change the environment of a horse & it will change the form of it's hoof? One recent study(we won't go into ethics, etc...) on this was done by the Australian Brumby Research mob, where they took a brumby mare from a 'cushy' soft, well fed environment and put her out in the central desert(somewhere near Alice) to join a mob of ferals there. She apparently did it really tough for a while, wasn't up to keeping up with the locals, but eventually she adapted & when they caught her many months later, she had developed the short, tough, 'rock crunching' sound feet of her new band.
There have also been many egs of domestic horses with problem feet/chronic lameness coming good in different environments/management, of various breeds. For eg explorers & stockmen in the outback who have had to leave lame beasts behind, only to find them months or years later, sound & well, as well as countless 'strong footed'(supposedly genetically stronger) ferals developing the myriad of 'domestic' problems when kept/worked in that environment.
I find the genetic argument about ferals also unlikely, when you consider that in Australia at least, they are - or at least recently(far too recent for evolution) were - domestic stock. Even to this day, horses are released to breed, released because no longer needed, or not yet needed, etc. Somewhere(I forget where) in the mountains not far from here, there are mobs of tough footed, chunky, palomino brumbies, because someone released a load of Haflingers a couple of generations back The same for the clydie type horses from the NT...