Grass tetany

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It's time for beef producers to start looking out for Grass Tetany!

Grass tetany is caused by decreased blood magnesium levels which in turn lowers brain magnesium levels, leading to convulsions, recumbency and ultimately death in lactating beef and dairy cows.

The reason for decreased blood magnesium levels can be due to a couple of predisposing causes.

  • Decreased intake of magnesium; low levels of magnesium in pasture, decreased fibre intake, decreased feed intake
  • Excessive potassium intake; recently¬†fertilised pasture with high levels of potassium fertilisers
  • Stressors in the environment; cold and/or wet weather

Grass tetany (Hypomagnesaemia) generally only occurs in lactating cows (3+ lactations), due to the increased magnesium requirements for milk production. Magnesium absorption can be interfered with by excess intake of potassium and decreased fibre in the diet, allowing faster passage of feed through the gut and decreasing magnesium absorption. 

Treatment for grass tetany involves injection of magnesium via the use of 'Flow Packs' such as 4 in 1, Minject etc which contain magnesium as well as calcium and glucose. These fluid packs can either be injected intravenously (following directions on the pack) or given subcutaneously. Even intravenous administration of magnesium takes more than 20-40 minutes to show a response due to the slow passage of magnesium from the blood stream to the brain were it needs to be to have effect. It is important for the animal to be moved to a sitting position so as not to regurgitate or cause damage to the head from repeated attempts to get up from the recumbent position.

Prevention of Grass Tetany involves supplementing magnesium in to the diet at regular intervals. This can be done in a number of ways.

  • Caus Mag, E Mag etc can be spread on hay as it's fed to the 'at risk' group. Generally 50gm of Caus Mag per animal per day is required.
  • Epsom Salts can be added to water troughs (MgSO4).
  • Dry licks containing magnesium and calcium can be used with free access for stock.
  • Bolus preparations can be given prior to calving to dispense magnesium through the at risk periods.
  • Increase hay/silage feeding through the at risk period to increase feed intake and slow gut passage.

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