Early spring is the season for grass tetany, and ranchers need to be aware of its causes and symptoms, and ways to prevent it.
Dr. Jeremy Powell, University of Arkansas Extension veterinarian, said grass tetany can become a problem in Arkansas during February, March and April, as cool-season forages begin to regrow. The disease is caused by an abnormally low level of magnesium in the cow’s body, and older lactating cows are more susceptible. Early symptoms include a decreased appetite, frequent urination, separation from the herd, increased excitability, muscle spasms and a stiff or unsteady gait; as the disease progresses, an affected cow will lose muscle control. This forces the affected animal to lie down, and it becomes unable to get up. “If your cattle are not checked often,” Powell said, “a dead cow may be the first sign of a problem.”
Powell told Ozarks Farm & Neighbor cows have no way to build up reserves of magnesium in their bodies. “They have to receive adequate amounts on a daily basis and it can be somewhat limiting, especially if they’re undergoing heavy lactation and grazing a lot of early forage growth,” he said. Ruminant animals absorb magnesium from the intestinal tract much less efficiently than do other species, and levels can be further reduced as the animal lactates and the mineral leaves her body via her milk.
The cows need to consume about 2-4 ounces a day of a free-choice mineral that’s 10 percent magnesium, and even that is not a sure fire method to prevent the disease. “High mag minerals typically are not very palatable,” explained Dr. Justin Sexten, University of Missouri Extension specialist in beef nutrition. “We want to make sure we get that out 30 days before grass tetany season, because by the time we see clinical grass tetany, getting the mineral out there and getting the cows started on it is probably too late.”
The problem is magnified in early grasses because they tend to be richer in potassium, which inhibits the cow’s ability to take up magnesium. Sexten told OFN high potassium can often be found in pastures that have had a fair amount of effluent or poultry litter spread on them. “You can address it is by using legumes,” he said. “Legumes are typically higher in calcium and magnesium, and that will help reduce the incidence of grass tetany while at the same time improving forage quality of the pasture.” The weather can also contribute to grass tetany; cloudy conditions decrease the plant’s ability to utilize magnesium, making it even less available to grazing animals, so tetany may be more often observed on cloudy or rainy days.
The disease is most often seen in older, high lactating cows, which have a more difficult time drawing needed magnesium from their bones. Sexten said if you see a cow exhibiting the staggering and convulsions associated with the illness, it’s important not to aggravate her. “If you stress the cow, you are more likely to cause her to die,” he said. “So, we try to minimize stress; the cow many times will be seen lying on the ground in a paddling motion, and if that’s the case the best method is just to call the veterinarian.” If the animal can be treated on the spot, she will likely recover; by the time she’s reached that stage, the stress of attempting to relocate her could be fatal.
