Caused by low blood concentration of magnesium and often complicated by a low blood calcium level. Most commonly seen in adult lactating animals grazing lush, fast-growing grass pasture, so should be uncommon in export animals. However, rare cases may be seen in the export process if accessible feed is low in magnesium or when other nutrients present in feeds such as potassium, protein or nitrogen interfere with the absorption and utilisation of magnesium in the body. The large need for magnesium in lactation means that even 2 days with little or no feed during early lactation may be sufficient to cause grass tetany. Therefore, it may be seen after transport, overnight yarding, or after stormy weather or stress that causes animals to go off feed for a period.
Clinical Signs and Diagnosis
Signs include muscle spasms, paddling convulsions and sudden death. Early or mild signs that may be seen include restlessness, frequent urination, drooling, stiff gait, and excitability.
Diagnosis is usually by clinical signs and response to treatment. Confirmation is by magnesium concentration in vitreous humour if sampled soon after death. Submit sample frozen.
Animals found with clinical signs require immediate treatment with magnesium sulphate solution injected subcutaneously, or a combined solution of calcium and magnesium given as a slow IV while monitoring heart rate. Alternatively, magnesium chloride or Epsom salts diluted in water given as an enema is also an effective treatment. Recovery should occur within a few hours, then feed legume hay or add magnesium supplements to feed to prevent recurrence.
As heavily pregnant and lactating animals are generally excluded from the live export market, this disease should be rare.