Grass Tetany

Knowledge Nuggets

• Grass tetany and winter tetany are caused by a magnesium deficiency which can occur when beef cattle are fed cereal straw, greenfeed or silage as a majority of the ration.

• Tetany can also occur when cattle are grazing lush, rapidly growing pasture and is characterized by nervousness, lack of coordination, and muscle twitching. Animals may become encumbered. If the animal is not treated quickly, the animal will die.

• Most forage in Western Canada contains adequate magnesium.

• High levels of calcium, phosphorus and potassium can interfere with magnesium absorption. The dietary K/(Mg+Ca) ratio should not exceed 2.2:1. High dietary K or Na sulphate or phosphorus reduces absorption of magnesium.

• Growing and finishing cattle need 0.1% of DMI as magnesium. Gestating cows need 0.12% and lactating cows need 0.2% magnesium. Maximum tolerable level is 0.40% of DMI.

• Mostly present in bone and muscle, magnesium functions in nerve transmission, genetic (DNA) formation and many enzyme reactions and also amino acid metabolism.

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