Grass Tetany in Cattle

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Grass tetany is a season-specific metabolic disturbance of cattle that occurs when cattle are grazing lush vegetation. It occurs mainly when cows are in transition from winter rations to grazing lush new growth pastures, but can occur in winter when cows are consuming poor quality hay or grazing small grains. The disturbance seems to arise from low levels of magnesium in forages. While magnesium deficiency is the culprit, some studies suggest that a phosphorous deficiency may prohibit plants from utilizing available magnesium. Either way, cattle are affected.

Signs of tetany include nervousness and incoordination, such as staggering or falling. Cattle may be easily excited during this period and muscle tremors and seizures become evident, with coma and death following. If you suspect that an animal is suffering from grass tetany, seek veterinary care.

There are several ways producers can help to prevent or limit losses from grass tetany. Producers can limit early grazing when grass is lush and young. Top-dressing pastures with magnesium is another option. Dolomitic limestone is a major source of magnesium. Also, feeding cattle a little extra amount of hay 7-10 days before turning out to lush pasture is an option. One of the best ways to combat grass tetany is to provide magnesium in a mineral supplement. There are many Hi-Mag minerals available, but look on the tag and make sure the supplement contains at least 14-15% magnesium. Cattle need to consume 4-5oz of magnesium oxide per day for best results. One note of caution, magnesium sulfate or Epsom salts is a great source of magnesium, however it is high in sulfur which can cause problems when feeding corn gluten feeds or distillers grains, which are also high in sulfur.

By taking measures in early spring, whether top dressing pastures with magnesium or providing a high mag mineral supplement, beef producers can reduce the incidence of grass tetany this spring and ensure that their herds emerge from winter and capitalize on spring forage growth.