Well the scientists say......
"Facial hair is largely governed by production of testosterone, which is known to be secreted by the testicles in greater quantities during and in anticipation of intercourse. Scientists have also found that increased beard growth was associated with tension, mental fatigue, alcohol and increased shaving. On the other hand, it is apparently curtailed by heavy exercise and high temperatures. "
So your beard grows faster out on the hill 'cause you're Randy, Apprehensive (probably from being caught with the sheep), knackered (from having sex with the sheep) and pissed (hence why you found the sheep attractive in the first place)