As spring approaches, grass tetany becomes a concern, cautions Bruce Anderson, University of Nebraska Extension forage specialist. Grass tetany is caused by low blood magnesium which can be due to low levels of magnesium in lush spring grass, but it also is caused by mineral imbalances like high potassium and nitrogen or low calcium in the diet.
Grass tetany primarily affects older, heavy milking cows or sheep, but young stock also can be affected. 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.
Anderson says producers can do several things to prevent grass tetany. First, wait until grass is four to six inches tall before grazing. Also, feed or graze legumes like clover or alfalfa when you start on pasture since they have high magnesium levels.
Adding about 10 to 20 grams per day of supplemental magnesium via commercial or home-made salt-mineral mixes is a good way to reduce tetany problems, but you should start as much as thirty days before grazing starts. Magnesium oxide is one of the best and cheapest sources of magnesium. Mix equal parts of magnesium oxide with dical, salt, and ground corn for a simple home-made supplement that provides adequate magnesium when cows eat about one pound of the mix per week.
Likewise, SDSU Extension Range Livestock Production Specialist Eric Mousel suggests cattle should receive at least .5 to 2 ounces of supplemental magnesium per head per day to prevent tetany. Magnesium is not effectively stored in the body therefore, supplementing more than two weeks before grazing does not improve effectiveness.
“Supplementing magnesium through a high magnesium block or mineral mix usually works best when livestock are out on range,” Mousel said. “Supplemental magnesium may also be added to protein supplements, silage, or as a liquid. Mixing magnesium supplements with a more palatable feed — for example, dried molasses, distillers grain, soybean meal — will help improve consumption.”
For more information regarding grass tetany, refer to SDSU Extension Extra 2055, “Prevention and Treatment: Grass Tetany.”