Grass tetany, or hypomagnesaemia, is caused by a deficiency of magnesium (Mg) in the blood. This is a rapidly fatal condition in beef and dairy cows and a common cause of sudden death – when an animal is found dead in the field without any history of disease or ill-health in the previous days.

Suckler cows and dairy cows have a poor capability to store magnesium in their bodies and must take in sufficient magnesium on a daily basis to prevent deficiency.