Grass Tetany is a condition that can effect stock in late autumn, winter and spring. It can cause significant losses in production, even when there are no signs of illness. Grass tetany (also called grass staggers) occurs when animals are grazing pasture which has low available levels of magnesium, or as a result of increased body demands for magnesium during lactation or late pregnancy. Prevention is preferable to treatment as grass tetany often occurs without warning. Prevention involves supplementing the animals with magnesium during the period of greatest risk.