The following is the Wikipedia paragraph I referred to in my first post:
"Modern conversions[edit]
In the 1960s, the Ortner Freight Car Company of Cincinnati, Ohio developed a triple-deck hog carrier for the Northern Pacific Railway based on the design of 86-foot (26.21 m) long "hi-cube" boxcar called the "Big Pig Palace." They later brought out a double-deck version called the "Steer Palace" that hauled livestock between Chicago and later Kansas City to slaughterhouses in Philadelphia and northern New Jersey until the early to mid-1980s on Penn Central and Conrail intermodal trains.
The Union Pacific Railroad, in an effort to earn more business hauling hogs from Nebraska to Los Angeles for Farmer John Meats, converted a large number of 50-foot (15.24 m) auto parts boxcars into stock cars. Originally built by Gunderson Rail Cars in Portland, Oregon for the Missouri Pacific Railroad, the conversions were done by removing the boxcars' side panels and replacing them with panels that included vents that could be opened or closed. The tri-level cars featured built-in watering troughs.
Strings of 5-10 of these "HOGX" cars were, until the mid 1990s, hauled twice-weekly at the front of double-stack intermodal freight trains. However, this service was terminated when Farmer John Meats shifted to hogs produced locally in California. The units have since been scrapped." (c) Wikipedia
I did not find any photos attached to the article that depicted any of the various pieces of rolling stock discussed. I am sure a determined search of the Net might result in a few pictures.
I am modeling the "stock yard switching district" of Oklahoma City. I know they still received shipments of livestock in the early 60s...BUT NOT MANY. By the mid 70s only one of the original 3 packing plants was still operational and it was a ghost of its former self. The only photos I have seen of the OKC Stockyards in the 60s showed stock cars that were the typical 36ft and 40ft wood slat cars we are most familiar with. Likewise, most of the reefers were still 36ft and 40ft ice bunker cars. Quite a few were still wood cars, but the majority were steel. Mechanical steel reefers were more common by the end of the 60s.
I elected to model 1963 so I could still run the zebra striped geeps and switchers, thus I can also run the wooden stock cars and the wooden and steel reefers.
If you are just modeling the mainline and the stock cars are "run thru" I believe the wooden cars would be rare after 1970. If you are modeling the industry and you are post 1970, I think you would probably not see many stock cars, if any, unless you are modeling specific markets.