Can a horse pen be an acute triangles?

Answer 1

Horse pens (also known as corrals) are usually square or rectangular, consisting of four right angles at the corners. However, I see no danger in keeping a horse in a triangularly-shaped pen.

Answer 2:

As stated above most pens are square or rectangular, they can also be circular. however a triangle, especially an acutely angled one does pose a danger if the horse gets trapped they can easily injure themselves in a tight space, especially if there is more than one horse in the pen due to the way herd dynamics work. Also tight spaces like those that would be found in the 'tips' of the triangle would cause the horse distress at some point as horses do not like being confined in tight spaces.