Grass tetany (hypomagnesemia) is a rapid-onset, often fatal condition in cattle caused by inadequate magnesium intake from lush spring pastures, causing severe neurological distress.
Grass tetany causes some of the most acute and distressing welfare events in cattle farming. The neurological crisis — from initial hypersensitivity and paddock pacing to full convulsions — is profoundly frightening and painful. Death can occur before stockpeople even recognize the condition has begun. Prevention is dramatically more effective than treatment: magnesium supplementation during the risk period costs very little compared to the welfare cost and financial loss of a tetany death. The seasonally predictable nature of the risk makes it an eminently preventable welfare problem, and failures to prevent it represent a management gap rather than an unavoidable hazard.