[JaeByrd]

We recently watched a documentary on wild horses. When herding them they release a "Judas Horse" that is trained to run for the corral and the other wild horses follow.

Sheep also being a herd animal have similar instincts:

Sheep follow each other so reliably that special names apply to the different roles sheep play in a flock. One calls a sheep that roams furthest away from the others an outlier. This sheep undertakes to go out further away from the safety of the flock to graze, while taking a chance that a predator, such as a wolf, will attack it first because of its isolation.

Another sheep, the bellwether, which never goes first but always follows an outlier, signals to the others that they may follow in safety. When it moves, the others will also move. The tendency to act as outliers or as bellwethers, or to stick in the middle of the flock, seems to stay with sheep throughout their whole life

I wouldn't call a bellwether, or outlier, a shepherd (or "under-shepherd") even though they "lead" the flock. The bellwether is just another sheep that is usually one of the oldest of the flock making it wiser to the hazards of the field. It leads not through driving the flock (like sheep dogs) but by example.

Calling a pastor a "under-shepherd" puts them outside of or above the flock.