Identification and prevention of Grass Tetany in cattle

As springtime progresses, cattle begin grazing cool season forages. Young, rapidly growing grasses are high in potassium leading to poor magnesium absorption in cattle. If not monitored closely, cattle can develop a fatal metabolic disorder called grass tetany also known as grass staggers. Lactating cows have the highest risk of developing grass tetany since they have high magnesium demands.

 

Although grass tetany can be difficult to identify in the field, there are several symptoms to watch for in cattle. Symptoms include increased excitability, teeth grinding, excessive salivation, muscle spasms, loss of body control, and in severe cases collapse and death. If cattle are presenting any of these issues, it is crucial to treat them immediately by contacting a veterinarian. However, prevention is the best method of management for this disorder, and strategies require attention in both supplementation and pasture management. 

 

Providing high-magnesium supplements such as “hi-mag” minerals which have between 6-10% magnesium. Magnesium oxide is primarily used in mineral supplements and is known to be undesirable to cattle due to the taste being bitter or alkaline. Because of this, grass tetany can still occur in cattle when given a magnesium supplement. Monitor intake closely to ensure cattle are meeting their magnesium requirements. Some cattle producers commonly mix magnesium into molasses or feed to help with palatability. Instead, consider increasing salt content in mineral. Sodium allows magnesium to become more available to cows when provided. If possible, locate a mineral with at least 30% salt or mix a bag of salt and a bag of mineral for cows in March and April. 

 

Lastly, do not apply high rates of potassium fertilizer in early spring. Since potassium competes with magnesium in the cow’s rumen, high inputs of potassium fertilizer can increase the risk of grass tetany. Also, consider overseeding legumes in pastures to help diversify cool season forages while providing higher magnesium levels. 

 

This information was provided by MU Extension state beef specialist Eric Bailey and state forage and grazing management specialist Harley Naumann. If you have further questions regarding grass tetany, please contact your local livestock or agronomy field specialist.