from Montana and a cowboy from California are on a sheep
drive. They have been out for weeks and have been pulling sheep out of the mud and working really hard. Eventually they come across a sheep with her head stuck in the fence.
They are both very lonely, so the cowboy from Montana says "I'm first!" and he drops his pants and mounts the sheep. When he is finished, he steps back, looks at the California cowboy, and says "You're next".
The California cowboy drops his pants and sticks his head in the fence.