In reply to Run_Ross_Run:
He probably asked because if there are loads of sheep even walking on a leash causes fear. Sheep don't see a leash and think 'great, fido is leashed'. If its lambing time and all the sheep are in a restricted area a dog walker should just avoid the field, even being in there causes mass stampedes.
I lived in or around Snowdonia for a decade and ran thousands of miles with my dogs off the leash. On the high mountain areas sheep are pretty rare these days. Hence why the law is under control.
You'll still see a lot of sheep on the valley sides lower down but once up they are limited how many can be there.