Hypocalcemic tetany in horses is uncommon but can develop after prolonged physical exercise, such as endurance rides, or transport (transport tetany) and in lactating or nursing mares (lactation tetany). A low level of calcium in the blood (hypocalcemia) can be caused by decreased absorption from the intestines, by increased loss through the milk, urine, or sweat, or by changes in bone metabolism. Producing large amounts of milk and grazing lush pastures make lactating mares more inclined to develop the condition.

Signs correspond to the level of calcium in the blood, and most relate to muscular spasms, tremors, and stiffness. Other signs include inability to chew, spasm of the jaw muscles, drooling, lying down, seizures, and irregular heart rhythms. In severe cases, synchronous diaphragmatic flutter may develop. In this condition, the diaphragm contracts at the same time as the heart to produce loud thumping noises (heard with a stethoscope) and usually visible contractions in the flank area.

Calcium solutions given intravenously usually result in full recovery. Some horses need repeated treatments over several days. Throughout pregnancy, mares should be fed a balanced ration that contains adequate amounts of calcium and phosphorus in the correct ratio. When calcium demands are increased, for example when nursing a foal, mares should be fed high-quality forage such as alfalfa or calcium-containing mineral mixes. Stress and fasting during transport should be minimized.

Last full review/revision July 2011 by George M. Barrington, DVM, PhD, DACVIM; David L. Evans, BVSc, PhD; Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM; Donald C. Sawyer, DVM, PhD; Ivan W. Caple, BVSc, PhD, MACVSc, MRCVS; Sharon J. Spier, DVM, PhD, DACVIM