April 20, 2006

Lush Pastures Can Lead to Grass Tetany

The lush, green grass of early spring can be very attractive to cattle and sheep.

However, it also can result in a condition called grass tetany, which can be fatal to the animals, a North Dakota State University Extension Service beef expert warns.

Grass tetany is caused by low levels of magnesium in the blood. The animals’ nerve impulse transmission fails when their magnesium levels are too low. Grass tetany can develop when cattle and sheep graze lush pastures because high levels of nitrogen (protein) and potassium in the forage can reduce the availability of magnesium, according to Greg Lardy, NDSU Extension beef cattle specialist.

The disease also is known as grass staggers, wheat pasture poisoning, magnesium tetany and hypomagnesia. It is more common in cows or ewes in heavy lactation, he says. It also can be more common when animals are grazing fertilized pastures.

Cool-season grasses, such as bromegrass, crested wheatgrass, timothy and bluegrass, and annual cereals, such as wheat, oats and rye, cause the most problems, Lardy says.

Affected animals tend to be excitable and may appear blind. They also may graze away from the main herd, appear wide-eyed and have muscular twitching in the flank, muscular incoordination and a staggering gait. Ultimately, they will collapse, thrash about, enter a coma and eventually die. However, in some cases, producers find their animals dead without seeing any symptoms.

Lardy says treatment is difficult because of the rapid onset of the condition. In some cases, intravenous infusion of calcium and magnesium in a dextrose solution can be effective. Producers should consult their veterinarian about a treatment.

“The best bet is to take steps prior to grazing to help avoid grass tetany,” Lardy advises.

Here are some techniques to prevent the disease:

• Encourage daily intake of magnesium. Magnesium oxide is the most common source of supplemental magnesium. Keep mineral boxes filled and scattered at several locations in the pasture.
• Make sure lactating cows receive 0.20 percent magnesium in the diet on a dry-matter basis. This is equal to 18 to 21 grams of magnesium intake daily.
• Use salt mixtures containing magnesium oxide as a magnesium source. To be effective, the mineral mix should contain at least 10 percent magnesium.
• Mix magnesium oxide with other supplements because it is unpalatable.
• Graze legume or mixed legume-grass pastures first because early, lush grass growth is more problematic than more mature forages.
• Graze less susceptible animals on problem pastures. Dry cows, heifers, stocker cattle and cows nursing calves more than 4 months old are less susceptible than cows in heavy lactation.

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Source: Greg Lardy, (701) 231-7660, glardy@ndsuext.nodak.edu
Editor: Ellen Crawford, (701) 231-5391, ecrawfor@ndsuext.nodak.edu

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