Grass tetany (hypomagnesaemia) is an acute metabolic crisis in cattle grazing lush spring pastures low in magnesium. It can cause rapid death but is largely preventable with magnesium supplementation.
Grass tetany causes acute and severe suffering. Affected cattle experience extreme neurological distress — muscle spasms, inability to stand, convulsions, and respiratory failure — often with a fatal outcome. The suffering is intense but brief in terminal cases; subclinical hypomagnesaemia may cause persistent anxiety and reduced milk production over longer periods. Prevention is straightforward and cost-effective, yet grass tetany remains common because supplementation programmes are inconsistently applied or overlooked during the rapid management demands of spring. Farmers who implement systematic magnesium supplementation protect their cattle from a genuinely agonising condition.