I believe this phrase refers to a parallel that the new testament implies regarding our Lord and Savior , Jesus Christ. More than once in the good book , Christ is referred to as the Good Shepard who...
oy ewe!
on farms yes but as a pet no they. where originally to protect the sheep
Do you mean the Van Gogh painting? If so, here it is in the related link. For actual photos of shepherds and sheep, see the Related Link below.
Maybe it was sick or lame or too weak to keep up with the others.