A helicopter can cause panic in any farm (or other) animal not used to them, especially if it appears suddenly and acts like a predator. Sheep will probably run away and then not be too fussed once you’ve shut down. Cows will come back and try to eat things or scratch themselves against the airframe.....not good! Horses are likely to run through fences if they feel trapped in a corner, so give them an easy escape route and time to find it. I once had my parked Puma damaged by a bolting horse....nothing to do with us, the aircraft had been parked in an Army barracks for some time. A couple of horses got out of their stables and ran through the barracks. One of them snapped our HF radio aerial cable off the side of the tail boom in passing.