During pregnancy, the cartilage of the pelvis softens and stretches to allow the foal to pass through. It takes several months after foaling for the pelvis and the muscles connected to it (psoas,adductor) to regain stability. During that time, injury to the pelvic area can happen very easily, especially when spring rains make the ground slippery. If your mare is standing wide behind, if she has little action in the hocks when trotting, if she has difficulty picking up the canter, she may need an adjustment of the pelvic area. Myofascial release and massage can reverse the condition, but rest will be needed. Recovery will take some time.