Cattle producers often consider grass tetany a problem that only affects cattle eating lush, spring grass. However, it can occur in dry-lot situations too, says Steve Ensley, a University of Nebraska Veterinarian.

"Any forage high in potassium has the potential to cause grass tetany," adds Ensley.

Interactions between key nutrients in a cow’s body can bring about grass tetany if the diet is unbalanced. "Low levels of magnesium can cause grass tetany. Magnesium enables a cow’s nervous system to function properly. Calcium, phosphorus and potassium are able to interact with, or tie up magnesium, which can lower the availability of magnesium – even if it is in the diet," he explains.

Cows with grass tetany may become overly excited, eat less and exhibit muscular twitching around the face and ears. They may also appear uncoordinated and walk with a stiff gait.

"Many times people see the symptoms but don’t think of grass tetany because the cows are in dry-lot situations or don’t have access to green growing grass," says Ensley.

An intravenous magnesium-salt solution can be used to treat animals with grass tetany. If grass tetany goes untreated, cows can go down on their side with convulsions, leading to death.

Don Adams, range beef nutritionist at NU’s West Central Research and Extension Center in North Platte, NE, says tetany will be occur with cows just before calving because of their diets.

"While the cow is getting ready to lactate and makes a bag, the magnesium is pulled out of the body and her serum magnesium level goes down," says Adams. "The free-choice minerals or hay in the cows’ diet are usually high in calcium and potassium. This combination will induce grass tetany."

To prevent problems, Ensley recommends cattle producers replace their current mineral if it’s greater than 1 to 2% potassium with a mineral higher in magnesium. He also suggests a mineral should contain 7-14% magnesium at all times. This translates to 10-25 grams of magnesium per head per day.