Grass Tetany - The Basics

Spring is just around the corner (I hope!) and when cows start grazing the new lush growth of spring grass we hear reports of cows becoming overly excitable, going into convulsions and dying. The time is now to provide supplemental magnesium to avoid the problem. Why?

Grass tetany is a nutritional or metabolic disorder characterized by low blood magnesium. It is also called grass staggers, wheat pasture poisoning, and hypomagnesemia. Grass tetany primarily affects older cows nursing young calves, but can also occur in young cattle, dry cows and growing calves. It is normally associated with cattle grazing lush, immature grass. Wet cloudy and cool springs are particularly known for grass tetany problems. We can also see problems with early fall growth after drought conditions.

Symptoms of grass tetany are excitement, loss of coordination, loss of appetite, irritability, muscular twitching in flank, wide-eyed and staring, staggering and collapse. Thrashing, severe paddling convulsions and coma follow collapse. Cattle on pasture are often found dead with froth from the mouth and nose, and the ground is rubbed where the animal has had convulsions before death.

Cattle require a constant intake of magnesium and only absorb one third of their magnesium intake from the rumen. Further complicating matters, cattle have a very limited ability to store magnesium in the body. Magnesium is rapidly excreted through the milk, urine and feces.

Prevention is the best form of treatment. New research indicates high phosphorus soils have plants with higher magnesium levels and lower grass tetany risk. Legumes either grazed or in hay are higher in magnesium and lessen the risk.

Another option is to feed supplemental magnesium just prior to and during times of high risk. Remember that magnesium needs to be consumed on a daily basis. Feeding magnesium oxide (MgO) is recommended as an economical product in which magnesium is readily available. For effective prevention, cattle need to consume approximately two ounces of MgO per head daily. Unfortunately, MgO is relatively unpalatable to cattle, and assuring proper intake can be a challenge. MgO can be added directly to your grain and/or protein supplement during periods of high risk. Or, diluting with loose salt, dried molasses or a protein supplement (soybean or cottenseed meal) will promote intake.

Remember, in general, the most critical time to supplement magnesium to cattle is when heavy milking cows have young calves on them and the grass is rapidly growing. Cows showing signs of grass tetany when excitable can be dangerous so BE CAREFUL!


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	Matt Herring - Agronomy/Natural Resources Ken Bolte - Farm Management/Livestock Franklin County University Extension Center Last revised: 11/28/05	Go to Franklin County University Extension Center page