Grass Tetany in Beef Cattle
Darrell Rankins, Jr.


The dogwoods are blooming, the fish are biting, Spring is upon us, have you prepared for the potential problem of grass tetany in your cattle. Grass tetany is primarily a problem during this time of year when cattle are grazing highly fertilized grasses or cereal crops. It is a result of a serum magnesium deficiency in the animal. Grass tetany generally occurs in females during early lactation; however, other classes of cattle can also be afflicted. Signs of tetany may not be noticed until the animal is already down or dead. Early signs may include: nervousness, salivation, muscle tremors and labored breathing. Ultimately, the animal will go into convulsions and die if treatment is not administered promptly.

Grass tetany is always associated with low concentrations of serum magnesium. Blood serum is low in magnesium because the cow is unable to absorb sufficient amounts of magnesium. This is a result of the forages being low in magnesium during this time of year, being high in potassium and nitrogen and low in dry matter content.

A mineral supplement containing adequate magnesium is the most reliable means of preventing grass tetany; however, the cattle must eat the mineral. Cattle should consume 1 to 2 ounces of magnesium per day and their intake should be monitored frequently. Daily consumption is important because magnesium is not stored in the body for very long.

Several commercial mineral supplements are available which provide adequate amounts of all minerals and additional magnesium. At least 12 percent actual magnesium is recommended. The most economical means of supplementing magnesium is a 1:1 mix of trace-mineral salt and magnesium oxide. In general, magnesium oxide is not very palatable and the cattle may not consume enough of this mixture. Consumption can be improved by mixing equal quantities (by weight) of ground corn, trace-mineral salt and magnesium oxide. Other palatable grains also may be used; however, do not use protein supplements or meals to increase consumption. The high nitrogen concentration will serve to aggravate the problem. Remember - the goal is for the cows to consume 1 to 2 ounces of magnesium per day and the magnesium oxide is 60% magnesium.

Treatment of grass tetany can be successful if quick enough. When signs of grass tetany occur, contact your veterinarian as soon as possible.