Tail Strings?

My Swiss "there must be a good reason for this" moment for the day. I was flicking tv channels and there I see a Swiss cow barn. Swiss cows will bells round there necks in a barn eating hay. Fair enough - I get that bit.

The puzzling thing - each cow had a rope attached - descending from the roof to the end of its tail. The ropes were reasonably tight so if the cow was lying down the end of the tail was sticking up in the air.

Why was this so? Fly strike prevention, cleanliness, a kind way of making sure the cows have to share there food. Why is this so?