Lush, green, rapidly growing grasses present a considerable risk for grass tetany, regardless of season. The combination of high potassium and low magnesium and calcium in these forages is thought to be the primary cause of grass tetany. Because of the increased forage production and growth rate, cattle grazing fertilized pastures are generally at higher risk. Legume pastures and legume hay are good sources of magnesium and calcium and are generally not a concern for grass tetany.

The most effective management strategy to address grass tetany is to prevent it. Prevention can be accomplished several ways. One method to minimize the risk of grass tetany is to delay turnout until the forage is more mature and is past the rapid growth stage. Delaying turnout will not only help reduce the risk of grass tetany, but it can also be quite beneficial to the range or pasture. This strategy works quite well, but may not be practical for some producers.

A more common management strategy to prevent grass tetany involves supplementing magnesium while the cattle are grazing higher risk forages. Cattle should receive at least .5 to 2 oz of supplemental magnesium per head per day to prevent tetany. Magnesium is not effectively stored in the body; as such, supplementation prior to the grazing period is not an effective prevention strategy.

The most practical means of supplementing magnesium under range or pasture conditions is through a high magnesium block, tub or mineral mix. Supplemental magnesium can also be added in combination with a protein supplement, silage, or a liquid. Because of the low palatability of magnesium supplements, care should be taken to insure that the cattle are consuming adequate levels of the supplement. If they do not consume adequate levels of magnesium from a free-choice mineral mix, the supplemental magnesium should be combined with a more palatable feed (i.e. molasses, distillers grain, soybean meal) to help drive consumption.

Regardless of the prevention strategy utilized, cattle should be observed at least twice per day when they are first turned out on spring pasture. There are some clinical signs that can be used as indicators of grass tetany; however, the first sign is usually a dead animal. Animals with grass tetany frequently stop grazing and appear nervous or high-headed. They will likely respond quickly and erratically to the slightest stimulus. As the condition advances, they may begin to stagger or experience twitching of the skin, followed by stiffening of the muscles and violent jerking convulsions with their head pulled back. They may also lie down and “pedal” with their legs and chew to the point of frothing at the mouth. If the convulsions subside, the animal may appear more relaxed; however, noises or touching of the animal, even to administer a treatment, may result in violent reactions.

If an animal is suspected of having grass tetany, time is of the essence. A veterinarian should be contacted immediately to administer a magnesium solution intravenously. Frequently treatment can be given in range conditions. The response to treatment depends heavily upon how advanced the condition is at the time of administration.

Grass tetany is a potentially deadly condition in beef cattle. However, control and prevention can be accomplished quite easily with management and supplementation.