The female horse does not bleed during the cycle. So you don't need to worry about the floor getting dirty or filled with blood. And this is not the way to find out whether she's having her cycle or not.

What are the signs of a mare in heat?

Typical signs that the mare is in season include holding the tail elevated, "winking" (opening and closing) the lips of the vulva and variable amounts of squatting and squirting of urine and mucus. A mare's level of activity usually slows down a bit, and she often seems preoccupied.

Do mare horses have periods?

The estrous cycle, also known as "season" or "heat" of a mare occurs roughly every 19–22 days and occurs from early spring into autumn. As the days shorten, most mares enter an anestrus period during the winter and thus do not cycle in this period.