Grass Tetany Can Be Fatal for Cattle
Grass tetany (also known as hypomagnesemia or “grass staggers”), a disease that commonly occurs in North Carolina in the months of February, March and April, is due to an abnormally low level of magnesium in the cow’s body. It is most common in older beef cows that just have given birth to calves, but can affect younger cattle as well. This disorder is usually seen in the spring when livestock graze young and succulent cool-season grasses such as tall fescue, annual ryegrass, and small grains (wheat, oat, rye). Grass tetany intensifies in warm periods; especially 5 to 10 days after cool, wet, and cloudy conditions when lush, immature grass starts growing rapidly. When nighttime temperatures begin rising to 55 °F or higher, the incidence of tetany falls because grasses are more able to draw magnesium from the soil at warmer temperatures.
Lactating cows demand high nutrient intake, including magnesium and calcium. Magnesium enables a cow’s nervous and skeletal system to function properly. Cattle affected by tetany often graze away from the herd, eat less, are irritable, show muscle twitching around the face and ears, grinding teeth, excessive urination, staggering, and are somewhat wide-eyed and staring. They may also appear uncoordinated and walk with a stiff gait. When severe, the animal will collapse, thrash around, throw its head back, lapse into a coma, and possibly die. The onset of symptoms usually is quite rapid and affected animals simply may be found dead in the pasture. Oftentimes, when animals are found dead, there will be signs of a struggle nearby, the grass and dirt will be disturbed, where the animal’s head and feet thrashed about.
There is always concern for the prevention of grass tetany, particularly in early spring and late fall when lush pastures are available. Animals that have been down for 12 hours or longer are poor candidates for successful treatment; muscle damage may prevent these animals from rising even if their magnesium status is corrected. Treatment is often complicated by the severe nature of the animal’s convulsions and potentially aggressive behavior. The most important part of treating this disease is to correct the magnesium imbalance. This can be accomplished by administering 500 mL of an IV electrolyte solution (CMPK). This solution should be administered slowly, and heart and respiratory rate should be monitored closely. After treating with the IV solution, one can then administer one tube of CMPK gel orally or give another 500mL bottle of solution intraperitoneally to decrease the incidence of relapse. If clinical signs are mild, then Mg imbalances can be corrected by treating with approximately 150 cc of a 20 percent Mg sulfate solution given subcutaneously in several injection sites. When treating animals, practice caution to avoid being injured.
Prevention of grass tetany can be achieved by providing a salt-mineral supplement containing at least 10 percent Mg (14 percent preferred). Several mineral feeders should be used if stocking rates are higher for the herd. Mineral feeders should also be conveniently located in the pasture so cattle have adequate access to them. It is also important to review fertilization practices to keep this disease less prevalent. Fertilization should be based on recent soil samples taken from the farm.
Grass tetany can be a serious cattle grazing problem. Low blood magnesium may be caused by 1) a diet low in magnesium, 2) a diet with nutrient imbalances that interfere with magnesium metabolism, or 3) higher levels of milk production. Environmental conditions and management factors combine to result in pastures with low magnesium levels. Cool and wet soil conditions reduce the plant’s ability to utilize available magnesium, as well as high nitrogen and potassium levels from chemical fertilizers or manure. Because an outbreak of grass tetany can be so costly, prevention is the best course.
Source: Mississippi State University, University of Arkansas