I don't know. I trust my BO to feed my horses.
If they are "pastured" on a dry lot, I would assume Hay is being provided at the least.
Could it be that the horse wasn't being fed properly and that prompted the new barn? 

Also how would Cushings translate to "a disease because he was injected with so much during his racing years, that he now can't process the food he is given, and therefore its why he is this skinny."?  Honest question!!

There is a lot to this we don't know to be name calling.
I guess I am a neglectful owner as sometimes I do not see my horses for a week at time, sometimes more. 
I am battling a "skinny" horse myself.
(I is cranky today.)