What happens after the Bull Run (encierro) is over?

Immediately after the Bull Run, (encierro) heifers (vaquillas) are released in the bullfight arena (Plaza de Toros). They will chase all the runners who made it into the arena. It is less dangerous to be hit by a heifer, especially because their horns are taped. However, they can cause damage and one man was paralyzed from being hit.