Just use a regular 22 if you need to kill a predator in your pasture.
You won't scare the sheep.
Subsonics (not the various Quiet types) should kill very well and have very subdued reports with no "crack". RWS is my standard choice, about $8.00 a box ordinarily. Very accurate as well. I expect Eleys are about the same. The CCI segmented ones shoukd kill well, but haven't been nearly as accurate as the RWS.
Not a sheep or goat herder, but I would think predators running atround might alarm the little dears more than the occasional pop of a .22.
