Never heard of it or seen it with horses, but billy goats -- WOW! Look out! It is so stupid, it's hilarious -- as long as it's a small billy. I actually used to make a point of going out to see the billy goat before I took my shower. I would hold out my hand or just stand near him and he would instantly INSTANTLY be excited and within seconds he would emit! And again, and again, and again. ... There is a reason there's a saying, "as horny as a billy goat"!