Where do ex race horses go?

i have been following the various threads and also some side threads on Facebook etc. regards horse abuse and neglect

What has jumped out at me is the seemingly lack of visability into where ex race horses go.

So my questions are:

does the owner have any interest in where the horse goes? He paid to own the horse, he paid for it while he owned it. when does his responsibility end?

Does NHRA or other organisation have a register of approved vendors to get rid of horses post racing? they know who breeds them so makes sense they would care where the horse ends up.

is it acceptable that ex race horses are sent to slaughter houses after their careers or do we expect them all to run in green pastures in there old age? And if so what is the ethical approach to allowing the slaughter of horses?

Where do ex race horses go ? Anywhere and Everywhere ,