Dorsiflexion, or rounding of the horse's back happens when the horse defecates or urinates.
The pelvis flexes by tucking under itself, shortening the body length, bringing both legs closer to center of mass of the horse. http://flickr.com/photos/alf07/1555204834/ Same foal, not rounded: http://flickr.com/photos/alf07/1533605645/ Judy http://icehorses.net http://clickryder.com
