Hypomagnesaemia (grass tetany)

Grass tetany is caused by a number of interrelated factors; the end result is a drop in magnesium levels in the cerebrospinal fluid (the fluid surrounding the brain and spinal cord).

It is more a problem in mature and/or lactating cattle, but certain environmental condition can result in cases occurring in all classes of cattle. Conditions that can contribute to grass tetany are:

• Cold soils
• High potassium (potash) levels in the soil and the pasture
• Grass dominant pastures
• Low dietary sodium (salt), calcium and phosphorus levels
• Lack of mature pasture

Cold soils generally have more nitrogen in the form of ammonium, which can affect the ability of livestock to absorb magnesium. Potassium levels in young growing grasses are invariably high and this is a major factor in the onset of this condition.

Grasses can also be low in calcium and sodium, which increases the risk of grass tetany. Hence, the disorder is not often seen on clover dominant pastures, as they contain higher levels of calcium and sodium.

The efficiency of cattle to absorb magnesium from the rumen is approximately 18 to 22% on grass pastures. This availability can rapidly fall to almost zero under the conditions described above.

Symptoms of grass tetany include:

• Nervousness, twitching and high stepping
• An irregular gait
• Muscle tremors and spasms
• Convulsions
• Death

 

There are several options available to help reduce the risk of grass tetany:

• Adding magnesium oxide to conserved forage (hay, silage)
• Magnesium Block
• Magnesium Capsules

 

When using magnesium oxide with conserved forage, ensure cattle are consuming the magnesium oxide and feed with salt to improve the absorption efficiency of the magnesium. Rumevite® Magnesium Blocks contain salt, phosphorus and magnesium in a palatable molasses base, whilst Rumetrace® Magnesium Capsules (developed by the CSIRO) are intra-ruminal devices that continue to release magnesium for 60 to 90 days once inserted. These products will aid in the prevention of grass tetany.