Please share your theories on why a group of heifers will mount each other in simulated sex. I could imagine a group of young bulls attempting it (or sadly emasculated steers) because by nature, the males are the ones who do the mounting. But heifers will mount each other, too. This makes no sense.
(We used to tell the city kids that the cows were giving each other piggy-back rides.)
It ain't just heifers. Female dogs will do the same. The hierarchical dominance theory suggested might just be the ticket. I have seen female dogs exhibit this behavior towards another female in heat. Something about the pheromones seems to act as a trigger. Dogs are also hierarchy dominated so maybe that's it.