A cow-catcher is a head latch for cattle that holds them in place so that people are able to vaccinate the cow or help her give birth.
During my time as a ranch-hand I was asked to build this one out of scrap metal. It is able to hold a 1500 pound cow without any problem at all.
To use, the cow is directed into the catcher where, when she pushes on the gate with her shoulders, the two flaps latch catching her. When the work with the cow is done a person simply pushes down on the handle and the gate will allow the cow to move away.
This project probably took a little less than a day to finish but it will be standing for the next twenty years.