Grass Tetany – Prevention and Management

Grass tetany – or Hypomagnesaemia – is a serious, and often fatal metabolic disorder caused by low levels of magnesium in the blood serum of cattle, sheep or horses. Magnesium is a mineral that is required by all animals, and functions as an enzyme cofactor.

It is very important to the central nervous system because it competes with calcium in the excitation-secretion coupling process.

Grass Tetany is often referred to as grass staggers, and typical signs begin with an uncoordinated gait and terminate with convulsions, coma and death. Other signs of grass tetany include nervousness, twitching, staggering and animals lying on the ground and kicking due to muscle tremors.

High nitrogen fertilization is one of the contributors to low levels of magnesium – particularly on soils high in potassium or aluminium. The cool, cloudy wet weather of autumn, together with frosts and freezing temperatures, may cause acute spikes of potassium and nitrate in grasses. These can cause grass tetany in stressed animals due to weaning, malnutrition or disease.

Magnesium is not readily stored in the body to any great extent. It exists in the bones of the animal, but is poorly released from these stores. It is very important, therefore, that supplement magnesium is provided as a preventative approach to avoid any risk of this fatal metabolic disorder.

The economic effect of sub-clinical magnesium deficiency must not go unnoticed as milk yield and health of animals can be significantly affected.

There are many strategies that can be used as a preventative approach to combat grass tetany in animals. Pasture dusting can be completed on a daily basis at a rate of 7-10 kilograms of calcined magnesite per acre.

This is a reliable method if animals are not being supplemented with other sources. Sweetened calcined magnesite can also be used to increase palatability when dusting paddocks.

Magnesium salts can be incorporated into water troughs through dispensers – these are very efficient and can be used to boost trace element inclusion. The only disadvantage of this method is that in wet weather, animals may not drink water from the trough.

High-magnesiummolassed mineral blocks can be used effectively to prevent grass tetany at grass on a free-choice basis. Magnesium boluses may also be used to help prevent grass tetany – they can release magnesium on a daily basis either slow or pulse releasing.

The surest and the most reliable method in the prevention of grass tetany is the incorporation of calcined magnesite in concentrate feed. It is critical that the level of magnesium in the concentrates offered match the feeding rate offered to animals.

Excess magnesium will cause scouring in animals, which must be avoided. It is very important to consult with a qualified nutritionist regarding inclusion rates of calcined magnesite in concentrates to prevent grass tetany.