They respond well to rest, a gradual return to a graduated training regime, and balancing the diet. Other horses will suffer from chronic episodes of tying-up that can be debilitating. Our research suggests that there might be several inherited reasons for chronic tying-up. Certain lines of Thoroughbreds seem more susceptible to one form of tying-up that has a basis in abnormal regulation of muscle contraction. Muscle contractions are initiated by propagation of electrical impulses along the outer cell membrane and along membranous connections extending into the cell, which then stimulate the release of calcium from intracellular membranous storage sites.
Muscle relaxation requires energy-dependent pumping of calcium back into storage sites.
Our research indicates that a common cause of tying-up in Thoroughbreds is an inherited abnormality in the way calcium is regulated by membrane systems in the skeletal muscle. The narrow genetic origin of Thoroughbreds and the common lineage of the pedigrees of horses with tying-up would support the possibility of an inherited trait. The disease might lie dormant unless specific factors trigger the calcium regulatory system to malfunction. Triggering events include stress, excitement, lameness, high grain diets, and exercise at submaximal speeds. Young fillies are most commonly affected and usually are the most nervous and high strung.