As producers begin turning their cattle out on the green pastures of the Ozarks this spring, they should be aware of the harmful effects too much of the lush ground cover could have on their cattle.
Grass tetany results when magnesium and calcium levels in forages are too low to meet the requirements of cattle, and cattle do not receive adequate magnesium and calcium supplementation, said Tom Troxel, professor and associate department head of the animal science department with the University of Arkansas Division of Agriculture Cooperative Extension Service.
Ryegrass, small grains (e.g., oats, rye, wheat) and cool-season perennial grasses (e.g., tall fescue, orchardgrass) grown on soils deficient in magnesium, wet soils or soils low in phosphorus but high in potassium and nitrogen may contain very low levels of magnesium and calcium.
Troxel said that spring is an especially dangerous time for the condition because it is the time of the year when many spring calves are born and nursing.
“Grass tetany most commonly affects lactating cattle, particularly the highest-producing animals in the herd,” he said. “Magnesium and calcium requirements of lactating cattle are far greater than those of non-lactating cows. This predisposes cattle to grass tetany during lactation.”
Troxel said the disease is especially apparent in older lactating cows and more commonly affects cows with either very poor body condition scores or cows that are overconditioned. He said cloudy, misty and/or cold conditions and stressors such as hauling, penning or heavy lactation are other factors that can cause grass tetany.
Producers should look for nervousness, muscle twitching and staggering in their cattle. Troxel said an affected animal might even go down on its side and experience muscle spasms and convulsions.
“Clinical signs associated with this disease range from slight changes in behavior to death. Early in the disease, cattle affected by grass tetany may show signs such as decreased appetite, decreased milk production, tendency to stay away from the herd, increased alertness and a stiff or unsteady gait,” he said. “As the disease progresses, cattle may become recumbent and unable to get up. They will exhibit muscle tremors, a protruding third eyelid, increased pulse and respiratory rates and eventually death if untreated.”
Troxel recommends treating affected cattle intravenously with 500 ml of calcium borogluconate solution with 5 percent magnesium hypophosphate. He said the solution must be administered slowly, and heart and respiratory rates should be monitored closely during administration.
After treating with the intravenous solution, Troxel said to orally administer one tube of CMPK gel (a source of calcium, phosphorus, magnesium and potassium) or intraperitoneally administer another 500 ml bottle of calcium borogluconate solution with 5 percent magnesium hypophosphate for slow absorption to decrease the possibility of relapse.
Dona Funk, livestock specialist with the University of Missouri Extension, said that although there is a cure for grass tetany, there could be grave consequences for letting the condition go untreated for too long. The longer an animal goes untreated, the harder it is to recover, and without treatment, death can occur within several hours.
“The success of treatment varies greatly depending on the stage of the animal at the time of treatment,” she said. “If treatment is started within one to two hours after clinical signs develop, the animal will probably recover quickly and fully.”
Funk said that with the large amount of rainfall the area has received in the early stages of this spring, producers should be especially conscious of the condition’s threat to cattle. She said there are several methods of preventing grass tetany that could save producers time and money down the road.
She recommended limiting exposure to young grass or feeding roughage to cattle for the 10 days to two weeks before turning them out. However, she said the most common method of prevention is adding .5 ounce to 2 ounces per head of magnesium oxide to a supplement or mineral each day.
“It is important to remember that magnesium is not stored by the animal, so it is crucial to make sure the animal gets a steady supply of the supplement,” Funk said. “Tests have shown a rapid drop in blood magnesium just two days after supplemental magnesium was removed from the diet, so just feeding magnesium once or twice a week will not successfully prevent grass tetany.”
Funk said that if producers have questions about preventing or treating grass tetany, they should contact their local veterinarian or extension office.
