Grass tetany occurs when there is not enough magnesium in the blood, as adequate magnesium levels are required for proper brain and nerve function.
Information provided by Murray Local Land Services lists grass tetany as a leading cause of death for adult beef cows in South-eastern Australia.
It mostly occurs from late autumn through winter in lactating cows.
“The magnesium status of cows depends mainly on the balance between the amount of magnesium absorbed from the rumen and that lost in the milk,” the information states.
“Any excess magnesium absorbed is excreted in the urine.
“Grass tetany results when the output of magnesium exceeds the input. Magnesium intake depends on the level of magnesium in the feed and the amount of feed consumed.
“Generally, young grass and lush cereals have lower magnesium levels than older grass and cereal crops.
“Grasses and cereal crops have lower magnesium levels than legumes - eg clovers and lucerne.
“A sudden deterioration in weather conditions can lead to severe outbreaks of grass tetany by dramatically increasing the number of cows deficient in magnesium.
“Producers need to be aware of the risks and take steps to prevent this disease in lactating cows.”
Animals with grass tetany become nervous and excitable.
They may show muscular twitching, walk with a high goose-step or a staggering gait, bellow, go down, paddle and die.
Because of the short duration of clinical signs, affected animals are frequently found dead.
“Cows may become aggressive and so measures to avoid personal injury should be taken if the condition is suspected,” the information suggests.
“Magnesium deficiency alters calcium metabolism and thereby increases the risk of ‘milk fever’ in recently calved cows at pasture.
“The diagnosis of hypomagnesaemia can be confirmed by post mortem in most cases.
“It is important that a veterinarian is called upon in an attempt to reach a diagnosis in down cows and cases of sudden death, as other conditions may be hard to distinguish from grass tetany and require different remedies and prevention.”
Landholders are urged to consider magnesium supplementation as a preventative method.
Soil testing to check for at risk paddocks should also be considered.
For assistance, contact the Murray LLS on 1300 795 299.
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