Watch for Grass Tetany This Spring

Drought conditions this spring in much of western North Dakota are limiting forage growth, but grass tetany still is a possibility.

Grass tetany is more likely in pastures with little litter or standing forage from last year, according to Greg Lardy, North Dakota State University Extension Service beef cattle specialist and professor in the NDSU Animal Sciences Department.

Early grass growth often contains low levels of magnesium. When cattle or other livestock consume these forages, they can develop a condition called grass tetany, or hypomagnesia. As the term implies, cattle with this condition have low blood levels of magnesium.

The most common symptoms associated with magnesium deficiency are excessive urination, muscle spasms and staggering, as well as erratic and nervous behavior.

The onset of symptoms usually is quite rapid and affected animals simply may be found dead in the pasture. Cows in early lactation may be more severely affected since the demands of lactation further contribute to mineral imbalances, Lardy says.

Cool-season grasses, such as crested wheatgrass or bromegrass, and annual forages, such as ryegrass or wheat, often have been associated with grass tetany. They generally have high protein and potassium levels, which can worsen the problem, and low levels of magnesium. In some cases, native pastures with limited amounts of litter also can result in grass tetany cases.

“If grass tetany is a common problem in your herd, consider increasing the magnesium level two weeks prior to the spring turnout date by adding magnesium oxide to the diet,” Lardy advises. “It is not particularly palatable, however, and should be blended with more palatable feedstuffs to encourage adequate consumption.”

Producers should offer their cattle commercial mineral mixes containing 10 percent to 15 percent magnesium when the animals are grazing lush forages.

“The good news is that problems with grass tetany generally diminish as summer approaches and forages begin to mature,” Lardy says.

NDSU Agriculture Communication