Buck runs over the tracks of Slim and the cattle to confuse the cows. When the cows arrive, however, all the tracks are cattle hoofprints. (In the DVD audio commentary, the filmmakers explain that originally Slim, not Buck, was to scramble the trails; the backgrounds were from this original version.)
When Alameda Slim is branding the map of all the foreclosed ranches he has bought, he brands the Dixon Ranch (the previous home of Maggie, the Cow). Cut to a close-up of the map and the brand is gone, then reappears several seconds later.
With the Willy brother sitting in front of Slim's map, Little Patch of Heaven doesn't show up, ever, until Slim moves the character out of the way. The outline of Little Patch of Heaven should show up, for instance, while the camera is pointing straight at the boy's face, however, it's not there.
The plan is to put 5,000 cattle on one train. Using the standard 36 foot, one deck, stock car common to the steam era, that would require a train about three miles long. The train they showed did not have enough cars (or engines).