I have a Soay ram whos always 'loose' in summer, starts as soon as the first grass comes through and doesn't stop til late Autumn. Very frustrating but I think everyone is right, it's just him. Luckily he's never had fly strike because of it, probably cos he sheds his fleece.
He seems to have passed the problem to one of his sons too so I'm afraid thats him retired from the breeding plan.