NDSU Extension Service, Published May 17 2010
Grass tetany possible this spring on ND pasturesFARGO - Cool temperatures and sufficient rainfall (greater than average in some regions) have many North Dakota pastures set for abundant forage growth this spring.
Weather forecasters predict a substantial warming trend in the next several weeks, and rapid forage growth likely will 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 Carl Dahlen, North Dakota State University Extension Service beef cattle specialist.
Grass tetany, or hypomagnesia, is caused by low blood levels of magnesium and is most prevalent when cows and ewes in heavy lactation graze lush spring growth. Rapidly growing forages have low levels of magnesium, and the availability of magnesium is further reduced by high levels 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 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 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 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 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 to tetany than cows in heavy lactation.