When everyone shows up at the cattle drive, Curley introduces his wife. After Curly and Mitch help the pregnant cow give birth, Mitch asks Curley if he'd ever been married, Curley's response is no. Apparently, both of them had forgotten that Curley had already introduced his wife before the cattle drive started.
When Mitch is talking to his wife on the plane, an extra in the background can be seen performing the same action twice in two different shots. The extra moves from his seat in the right of the screen to the left (implying he is going somewhere), and then it quickly cuts to Mitch, then back to wife and the same extra is getting up from his seat and performing the same action all over again.
After the cattle drive is over, Clay says, "Let's get some grub". Ira, Ben and Steve, Barry, Cookie, and Bonnie follow, in that order. But when they switch cameras, their order is Barry, Ira, Bonnie, Ben and Steve, and Cookie following Clay and Millie towards the house.
(at around 1h 30 mins) As Mitch, Phil, and Ed are herding the cows down the slope and into the river (when Ed is already midway across the river), if you look to the extreme left of the frame (in the DVD wide screen format), you can see a man at the base of the slope. He momentarily darts into frame and back out again.
At the end of the movie Bruno Kirby says something like 'next year we are going to follow Admiral Byrd's route to the North Pole.' Actually, it was Admiral Peary who was credited with being the first person to go to the North Pole. Admiral Byrd was more famous for his solo, over-winter stay in Antarctica at his base called Little America.