Grass Tetany at Spring Turn-Out

BY Adele Harty, South Dakota State University Extension | | Comments (0)

The moisture from the spring snowstorms 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.

Older, lactating cows with calves younger than 2 months of age are the most susceptible to tetany; while steers, heifers, dry cows, or cows with calves older than 4 months of age are less susceptible. Mature cows are more susceptible because they are less able to mobilize Mg from bones to maintain the necessary level of Mg in their system. Also, cows that are less than two months after calving have increased milk production and require additional Ca and Mg.

Cattle will exhibit symptoms of grass tetany, but they may not be observed as death may occur within 4 to 8 hours. If an animal is affected by grass tetany, there is a series of progressive signs that an animal will exhibit. These include grazing away from the herd, irritability, muscle twitching in the flank, wide-eyed and staring, muscular incoordination, staggering, collapse, thrashing, head thrown back, coma, and death. Affected animals should be handled in a quiet manner, since sudden death can occur if animals are stressed.

There are treatment options for animals, but the effectiveness of treatment depends on the clinical stage when treatment is administered. If treatment is started one or two hours after clinical signs develop, the results are usually a quick recovery. If the animal isn’t treated until the coma stage, it is too late for the treatment to be effective. The normal treatment for grass tetany is intravenous injection of a commercial preparation of magnesium and calcium in a dextrose base from a veterinarian.

Remember that cattle are more susceptible to grass tetany in the spring of the year, and certain weather conditions increase it. Take into consideration and implement prevention practices, monitor cattle for signs of grass tetany, and treat them as soon as possible according to a treatment plan developed with a veterinarian.

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