Find where they feed and put up a wall of fence and corn on one side, this takes time.
As they eat the corn regularly put up a second and third wall leaving one side open, keep adding more corn.
After an extended period put up the final wall with a gate opening and the gate open, lots of corn, they are now used to the walls and the little ones it's all they know, food is found near the walls.
Whenthe whole herd is inside, slam the gate. They will mil about for a bit and a few may try escape but they have forgotten how to forage so they are dependent anyway, they quickly grow easy with their imprisonment and barely take note as one is cut from the herd for slaughter.
Thought for the day. Freedom is lost when those who work for a living are out numbered by those who vote for a living.