Kinda have that one reversed, don't you?
Feeder Cattle, prior to the index, used to be a 650 pound English breed to make or take delivery, ready to put on to the feed lot .... NOT a "fat".
Today, it is an index average of several auctions, of not only English breeds. Rather, those that could be placed on feed (put in a feedlot) and, for the proper time and ration, be raised to a "choice" (not Holstein choice) level. In other words ... those to come off grass, ready for the feedlot.
Live cattle, or fat cattle, are still a deliverable commodity. Although, they no longer need to be an English breed ... to be deliverable at par (no discount) they fall into a fed weight range, slaughter ready ,and graded choice.
Delivery specs for fats (live cattle) and the auction index explanation may be found on the CME's site.
