The moisture from the spring snow storms has given the grass the jump start it was needing. One challenge is that the grass will grow rapidly, so cattle producers should plan to prevent grass tetany in their herd. 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.
Multiple factors play a role in causing grass tetany, including:
- 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
- Various combinations of the above factors resulting in low blood Mg or Ca
The key to prevention of grass tetany is being proactive. Measures can be taken to minimize the risk associated with cows grazing lush pastures. Including legumes in pasture mixes will decrease the incidence of grass tetany, as these plants have higher levels of Mg and Ca than do immature grasses. If possible, grazing should be delayed until plants are 4 to 6 inches tall. This will reduce the occurrence of tetany, in addition to giving drought-stressed pastures a little more time to rest. The challenge with this is that many producers have to utilize pastures when grasses start to green up and tetany is most prevalent.
If delayed grazing is not an option, other management tools should be utilized. First, always provide a high Mg supplemental mineral, or mineral mix containing at least 8-12% Mg beginning two to three weeks before tetany is likely to occur. Palatability and consumption can be challenges, resulting in some of the animals consuming an inadequate amount of the mineral on a daily basis. Be sure all animals have access to the mineral while they are grazing tetany-prone pastures, as this will help decrease the occurrence of tetany. Another potential tool is to provide dry forages while cattle are on lush pastures; however, cattle are not likely to eat them unless they are forced. Dry forages can act as carriers to provide additional Mg and Ca to the animals at a critical time. If the drinking water source can be controlled (i.e., water tanks), soluble Mg salt may be added to the water. Some examples of 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 and therefore cannot be used for this purpose.