The signs of grass tetany, or hypomagnesaemia

What is it?

Grass tetany is rigid paralysis as a result of low levels of magnesium in the blood, leading to cows becoming recumbent (going down).

Predisposing factors

Rich, lush, well-fertilised pasture, stress factors such as weaning (sucklers), poor weather conditions and hunger.

Unlike milk fever, this condition is not associated with calving, although low blood magnesium can complicate milk fever.

Cows have limited stores of magnesium in the body, and require daily intake of the mineral, especially in periods of challenge.

What does grass tetany look like?

In the early stages, affected cows tremble and shake. As the condition advances, the cow goes down and starts to convulse and thrash. This condition can advance quite quickly to death if left untreated. Grass tetany is a common cause of sudden death in cows. A feature of such cases is the ground may be marked by the thrashing.

How is it treated?

Intravenous calcium injection and subcutaneous injection of magnesium is required for treatment. The prognosis decreases significantly if there is a delay in treatment, and therefore prompt treatment is crucial to avoid fatalities. Cows that are thrashing need to be sedated.

Prevention

Magnesium supplementation during periods of high risk is the key to the prevention of grass tetany. This can be achieved by feeding concentrates high in magnesium, administering magnesium boluses, pasture dusting with magnesium and supplementation through the water supply. Pasture dusting and water supplementation may not be reliable in wet weather.

Read more

Grass tetany - what you should look out for

Vet’s corner: Grass tetany an emergency issue