Grass Tetany in Cattle

— Written By and last updated by Elisabeth Purser
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Cows grazing in a field.With spring weather comes new grass growth and along with it the potential for grass tetany for cattle. Also called ‘grass staggers’ this condition is caused by a magnesium deficiency. This deficiency can be caused by a diet low in magnesium or a disruption in the body’s ability to process magnesium. It is most often seen in the spring when the grass is rapidly growing. Fresh, immature forages are lower in magnesium and higher in nitrogen and potassium, which can interfere with magnesium absorption in the rumen. Additionally, spring grass has a high water content which can dilute the nutrient content of the forage. Older animals and animals in early lactation also have higher magnesium requirements and are more susceptible to grass tetany. 

Symptoms are often not noticed until the animal is found dead in the pasture. Since this condition affects the nervous system, signs to be on the lookout for include standing away from the herd, a wild stare with alert ears, twitching, incoordination and staggering, followed by collapse, coma, and death. Treatment is only effective in the early stages, within an hour or two of first noticing symptoms. By the time the animal has reached a coma it is typically too late to save them. Treatment usually includes giving an injection of magnesium. 

Prevention is the best way to handle grass tetany. Wait to graze pastures until forage height is at least 4-6 inches. Younger more immature forages have less magnesium. Turn out your less susceptible animals, such as stockers, dry cows, and heifers, on higher risk pastures. You can include legumes in your fields such as clover. Legumes have higher magnesium content and can help mitigate grass tetany. Finally, you can offer your herd magnesium supplements during higher risk periods. Magnesium is not stored in the body, so supplementation must be done daily before and during periods of high risk. You can offer magnesium oxide, which is a good source of magnesium. However, it is unpalatable so mix it with something more palatable to encourage consumption. Another option is to offer a ‘high mag’ mineral free choice. 

Grass tetany is considered an emergency and requires immediate medical attention. Prevention is better for your herd than waiting until they need treatment. Be aware of what causes grass tetany and be ready to supplement your herd during periods of higher risk.