Tom, let me speculate: the CGW saw potential loads if they could provide
cars. Their stockcars dated from the teens or 20's and were worn out or
rotting away. The CGW had surplus single sheathed wood boxcars as they
upgraded to steel boxcars. Tax laws made it affordable to convert the
surplus boxcars into needed stockcars.
The CGW was not the only railroad to do this. The GN did it with their USRA
boxcars, which Accurail has produced in HO.
And lots of young cattle was moved from western grass lands (any dry lands
west of the Mississippi) to the feedlots of the Midwest where they were
fattened up on corn. Today we call this "value added" products