Know Conditions for Grass Tetany

Fodder for Thought

This spring's mild weather brings grass tetany concerns. Evaluate your risk.

Published on: March 22, 2012

It seems spring has arrived early this year. I spent the past week visiting my family in south-central Pennsylvania for spring break and it certainly felt like spring. Instead of the normal cool, rainy weather we have in March, we had temperatures in the 60s and 70s and it was continually sunny every day.

You’d have never guessed that exactly a year ago half the farm was under water due to flooding from torrential rains.

Our mama cows will be calving soon and the cool-season grasses are already off to a good start with the mild weather. This early lush forage growth coupled with calving sets the stage for grass tetany.

If you are unfamiliar with grass tetany, this ailment is caused by a low level of magnesium (Mg) in the plant, which leads a magnesium deficiency to develop in the bovine consuming the forage.

In reality, grass tetany, also known as hypomagnesaemia, only affects about 1-2% of grazing animals but should be considered as a serious concern in you have forages low in Mg.

There are many reasons why a forage grass may be low in Mg. High fertilization of grasses with potassium (K), also known as potash, depresses Mg uptake in the plant. High amounts of nitrogen (N) can also increase the plant’s fatty acids which may also depress Mg availability. Low soil temperatures and high soil moisture leading to low soil oxygen content, in the spring or fall, may also decease Mg uptake in the plant.

An animal’s susceptibility to grass tetany increases five days after the mean daily air temperature exceeds 57 degrees Fahrenheit, following a period below this temperature. I’d say that the weather of late has been well above 57 degrees and that because of this abnormally warm spring weather cattle are more susceptible to grass tetany than they normally would be this time of year.

Symptoms of grass tetany in cattle include nervousness, hypersensitivity, muscle twitching, staggering and convulsions. If you notice any of these changes in behavior, contact your veterinarian immediately. A blood test to determine blood serum Mg level will need to be done. Mg values less than 1.0 mg/100 ml are considered critical in cattle. Normal levels are between 1.5-3.5 mg/100 ml.

As the old adage goes, “An ounce of prevention is worth a pound of cure.” This is definitely the case with grass tetany.

Beef producers can do two simple things to ensure that this ailment isn’t an issue in their herds. Provide a magnesium supplement, whether free choice or included in a feed mix, to ensure Mg deficiency does not develop.

Practicing sensible fertilizer management of pastures or hay fields is also of utmost importance. By avoiding excessive N fertilization in the spring and if applying manure, doing so in a responsible manner, to ensure that available K levels in the soil are not in excess will ensure that plants are able to take up available nitrogen in the soil.

By using these practical management strategies producers will lessen their risk of developing grass tetany in their herds.