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Grass Tetany Possible This Spring

Good growth of forage this spring could lead to grass tetany in cattle.

Sufficient rainfall (greater than average in some regions) has many North Dakota pastures set for abundant, rapid forage growth this spring.

“With this in mind, producers with cattle on pasture or planning their spring pasture turnout need to be aware of the possibility of grass tetany,” says Carl Dahlen, North Dakota State University Extension Service beef cattle specialist.

Grass tetany is caused by a magnesium deficiency. It’s most common when cows and ewes in heavy lactation graze lush spring growth. Rapidly growing forages have low levels of magnesium, and high levels of protein and potassium in the forage further reduce the availability of magnesium.

Animals with grass tetany may experience excitable and erratic behavior, blindness, muscle tremors, a staggered walking pattern and, ultimately, death. The onset of the condition can be very rapid, and the first symptom producers may see is a dead animal.

Forages most likely to induce grass tetany are cool-season grasses (crested wheat grass, bromegrass, bluegrass and timothy) and annual cereal grasses (wheat, rye, oats). Tetany also can occur in native range pastures when grass growth is rapid and lush.

Producers should consult their veterinarian about a treatment if they observe symptoms, Dahlen says.

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 in 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 to tetany than cows in heavy lactation.

NDSU Agriculture Communication - May 22, 2013

Source:Carl Dahlen, (701) 231-5588,
Editor:Ellen Crawford, (701) 231-5391,
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