Watch for grass tetany in North Dakota cattle this spring, warns Carl Dahlen, North Dakota State University Extension Service beef cattle specialist.

Cool temperatures and average-to-better-than-average rainfall have given North Dakota pastures good forage growth and warmer temps may mean more rapid growth to follow.

“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 Dahlen.

Grass tetany, or hypomagnesia, is caused by low blood levels of magnesium. It’s most prevalent when cows and ewes in heavy lactation graze lush spring growth. Rapidly growing forages have low levels of magnesium, and levels are further reduced by high amounts of protein and potassium in the forage.

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

Forages most likely to induce grass tetany are cool-season grasses (crested wheatgrass, 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 veterinarians about treatments if they see symptoms, Dahlen says.

Here are ways 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% magnesium in the diet on a dry-matter basis. This is equal to 18-21 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% 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 four months old are less susceptible to tetany than cows in heavy lactation.