Rye, wheat and triticale are about ready to graze, and such fields can be a great resource. But they can cause health problems in cattle, among them grass tetany, says Bruce Anderson, University of Nebraska-Lincoln (UNL) Extension forage specialist, in his recent “Hay & Forage Minute.”

Grass tetany is caused by low blood magnesium, which can be due to low levels of magnesium in lush spring grass. But it’s also caused by mineral imbalances, such as high potassium and nitrogen or low calcium in the diet, Anderson says.

The condition primarily affects older, heavy milking cows or sheep, but young stock also can be affected. And it occurs most frequently in spring during cool, cloudy, moist conditions when lush, immature grass starts growing rapidly.

Cattle or sheep affected by tetany often graze away from the herd, are irritable, show muscle twitching, awkwardness and staggering, and are somewhat wide-eyed and staring. When severe, the animal will collapse, thrash around, throw its head back, lapse into a coma, and possibly die.

As always, an ounce of prevention is worth a pound of cure, Anderson says. He advises to start by not grazing until grass is 4-6 in. tall, and feed or graze legumes like clover or alfalfa when you start on pasture since they have high magnesium levels.

In addition, adding about 10-20 grams/day of supplemental magnesium via commercial or homemade salt-mineral mixes is a good way to reduce tetany problems, but you should start as much as 30 days before grazing starts.

Magnesium oxide is one of the best and cheapest sources of magnesium, Anderson says. Mix equal parts of magnesium oxide with dical, salt and ground corn for a simple homemade supplement that provides adequate magnesium when cows eat about 1 lb./week of the mix.