I've been tryin' to get those ornery yakows back into the pen all day!”— Farmer, The Precursor Legacy
Herd the yakows into their pen was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. The Farmer's yakows got out of their pen when "some strange creatures tried to steal 'em earlier". Jak eventually herded them back into the pen for a power cell.
After herding all the yakows into their pen, the mission was temporarily renamed to Return to the Farmer.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Yee Haw!", completing this mission will reward you with a bronze trophy.
Herding all five yakows into their pen is a simple feat of walking up to each yakow and putting it between the pen and yourself. From there, they will automatically move in a direction away from you, meaning you must keep on the move to lead it towards the pen. Kicking and punching has little actual effect in terms of speed, but can be used to quickly force them to turn to the side.
The pen, which is next to the Farmer's house, has an open section in the fences in front of it, which is where the yakows will automatically go and enter once close enough. One inside a yakow will not leave the pen afterwards.