well i grew up on a farm and we had cattle and my mum and dad used to tell us they were dancing when we were little, (seriously), i've only just remembered about that when i read this post!
Cows come into estrus (heat) every 21 days or so. when they're in that condition and no bull is present they will often mount other cows, but will not let any cowsmount her. .. It's an instinct triggered by the smell of the one in estrus...Cows remain estrus for only about 18 to 24 hours...