Stormy weather and lush pastures increase the risk of grass staggers, particularly in older lactating beef cows. Magnesium cannot be stored so a constant dietary supply is essential.
Magnesium levels vary considerably in soil and grass. High levels of potassium and ammonia from the application of fertilisers disrupt the ability of cattle to absorb magnesium from their diet. Lush pastures are low in fibre and increase the rate of passage of food through the rumen, reducing the time for absorption. Reduced intakes during periods of bad weather also reduce the overall intake of magnesium.
Affected cattle may show excitability, muscle twitching and aggression, progressing to recumbency, seizures and death. Due to the rapid progression of clinical signs most often cattle are found dead.
If found in the early stages, treatment consists of intravenous calcium spiked with 50ml magnesium. The remainder of the bottle of magnesium is given subcutaneously. Sedation may be required to control seizure activity. Treatment will maintain blood magnesium levels for 6-12 hours. Concentrates and palatable forage should be offered following treatment to avoid relapse.
Prevention options include supplementing all water supplies with magnesium chloride (250g/100 litres of water), feeding high mag rolls or magnesium boluses.