Rich, if the price was better in Chicago than in St Paul, then yes you would see cattle on the move via rail in 1950. While much livestock traffic had moved to truck, rail was still a factor in your time period. Esp if the cattle was coming a long distance, ie western grasslands.
As cattle and sheep were raised on the grasslands of the GN & NP territory, you would see GN & NP stockcars going into Chicago. And yes you might see these cars east of Chicago. But be aware that west of Chicago major feed and rest stations existed, where livestock was unloaded. Sometimes the same car would be used for reloading, sometimes a different car was used as the original had already been used or sent for cleaning or returned as an empty. Online railroads would use their own cars when possible, or used a car being return to its owner railroad. Much would depend upon the shipper and routing selected. But it was possible to see cars almost anywhere.
Rochelle Swift plant: from earlier correspondence about this plant, it appears it was built circa 1948. And went through several owners. Notes indicate it was primarily hogs, but handled some beef. Most hogs would have been local, ie a 100 mile radius of the plant, hence the heavy use of trucks to move hogs by 1950. Cattle may have come further distances. Swift was a large company with numerous slaughter operations. They had livestock buyers across the country making purchases to keep their slaughter operations running. Some you might have hogs or cattle coming from some distance away, if the price was right.
Doug Harding
www.iowacentralrr.org