Unlike these days when you can drop by a store and get eggs and milk, on the trail, they had to bring the sources of these two items.
The travelers would bring along chickens and a cow or two. They needed them, not only for the trail, but for the place they would settle in Oregon. There weren’t stores they could go to when they got to their destination. They would have to travel a distance to get supplies once they were home.
The cows walked along with the people.
The chickens sat in a chicken coop in the wagon. I don’t know if they let the chickens out to stretch their legs and eat insects at the end of the day. I imagine they did so.
The chickens could eat cracked corn. The travelers could buy whole corn and pound it into pieces.
The cows could eat grass along the trail.

Most of the pictures are from Wikipedia Commons. I labeled the ones that were from other sources.

The map of the Oregon Trail  by, National Park Service.

A covered wagon  by, Gary Halverson, Oregon State Archives.

I found a picture of a hen house that is fenced by chicken wire. It is large, but it gives an idea of how the chicken coop was made.

By, Cacycle

A girl chicken on the move.

By, Lilly M

Next, are two pictures of eggs. One has white eggs and the other has brown eggs. The eggs inside of the shells are the same.

By, Batholth

By, Piasoft

A picture of whole corn.

By, Rasback

These are Jersey cows that give milk. They are in front of Charlotte’s Ice Cream Parlor in Whitley, UK.

By, Richard Kay

This is prairie grass.

By, Robert Lawton

A picture of milk by the  US Center for Disease Control.

The last couple of pictures are of two that would not be on the trail.

By Markus Koljonen

By, Richard Webb