Grass tetany: Be aware of the risk

If spring snows and rains develop as we need them to, grass will grow rapidly and is a concern for cattle producers.  Grass tetany is a metabolic disorder that is associated with lush pastures due to low levels of blood magnesium concentration, which results in nerve impulse failure in animals. 

There are a number of factors that are important in causing grass tetany.  These are listed below, and unfortunately many producers are currently dealing with them, or will be in the near future.   Factors leading to grass tetany:

• Low magnesium (Mg) content of rapidly growing grasses and pastures
• High potassium (K) content of rapidly growing grasses and pastures
• High crude protein content of grasses and pastures
• Bad weather, storms, stress, etc., that cause cattle to be “off feed” for 24-48 hours
• Lactation:  losses of Mg and calcium (Ca) in the milk
• Ammonia fertilization of pastures or grasslands
• Various combinations of the above factors resulting in low blood Mg or Ca

In order to prevent the negative, effects grass tetany can have on your herd, it is important to be proactive in prevention.  There are some measures that can be taken to minimize the risk associated with cows grazing lush pastures.  First of all, if you can delay grazing of the pastures until the plants are 4 to 6 inches tall, this will reduce the occurrence of tetany, unfortunately most producers have to utilize the pasture when the grasses start to green up and tetany is most prevalent.  If this is your situation, there are a few management tools to use.  First, always provide supplemental Mg and Ca to your cattle in a mineral mix.  The challenge with this is consumption, and depending on the size of the pasture and the palatability of the mineral, not all animals will consume an adequate amount of the mineral on a daily basis.  Be sure that all animals have access to the mineral during the time they will be grazing the tetany prone pastures, as this will help decrease the occurrence of tetany.  If your animals will consume dry forages while they are on the lush pastures, you can provide them with these feeds, which can act as carriers to get the additional Mg and Ca to the animals at a critical time.  Another management tool producers can use is to add a soluble Mg salt to the water, if the drinking water source can be controlled, i.e. a tank.  Some examples of the soluble Mg salts are magnesium acetate, magnesium chloride, and magnesium sulfate (Epsom salts).  The most common form of Mg, Magnesium oxide, is not soluble in water, therefore cannot be used for this purpose. Also, including legumes in the pasture mixes will decrease the incidence of grass tetany in animals, as these plants have higher levels of Mg and Ca than do immature grasses.