Here in rural Shropshire, DHFS Squirrels and Griffins use one of our fields for confined-area work. Three adjacent large fields have been frequently used for cattle by local farmers. This year we have had the pleasure of sheep for the first time. I can't imagine how farmers cope with the stink of a flock of sheep on a hot day.
I have never seen cattle take the slightest notice of helicopters. The sheep initially seemed to flock and panic as described by others but after the first few occasions stopped taking much notice. Yesterday they were lying down and did not even get up when a Griffin flew a couple of orbits, landed and took off almost directly over their field. It appears that they get used to helicopters quite quickly.