Three hours until death

Jun 24, 2011
by DTN

Grass tetany is one of those things that can hit when a producer least expects it— which is exactly what happened to Bobby Miller.

“I guess we’d been lucky until this past winter,” says Miller. “But then we lost five cows—three in one day.”

Unfortunately, the Lula, GA, cattleman’s experience isn’t unique. Even though he checks his cows religiously, grass tetany, a magnesium deficiency, struck quickly and made it impossible to save the animals.

“There can be only two or three hours between the initial onset [of tetany] and death,” says Purdue University Extension beef specialist Ron Lemenager. “That’s why prevention is the key.”

A complex combination of factors seems to bring on the condition. “The incidence of grass tetany is usually highest in the early spring,” says Lemenager. “Grass is lush, vegetative and has a high moisture and fatty acid content. Forages are usually low in magnesium and the soil is high in potassium and nitrogen. When a producer has fertilized with manure or a commercial fertilizer, it becomes even more of an issue.”

But grass tetany also seems to be prevalent during times of transition from cool, cloudy, drizzly days to warmer, sunnier days. Lemenager says, “It seems like the probability of grass tetany goes up when the nighttime temperature is below 55 F.”

Aside from weather and vegetation, the animals themselves can be factors. Some are more prone to problems than others. Older cows and those at peak lactation, with a calf under 2 months old, generally are considered most susceptible. And once an animal has suffered from grass tetany, even if it was treated and recovered, it always will be more susceptible.

Treatment can be difficult—even dangerous. Cows with grass tetany are highly excitable, making IV treatment with magnesium dangerous for the cow, producer and veterinarian alike.

While you obviously can’t control the weather, and green, vegetative grass is a good thing, you can help prevent grass tetany. The key is a high-magnesium mineral mix containing salt.

“The problem with the most common form of magnesium, magnesium oxide, is it is not very palatable,” says Lemenager. “Salt helps overcome some of the palatability issues. And salt, particularly the sodium part of it, is important in helping magnesium be absorbed.”

The Purdue specialist says magnesium sulfate is another common supplement and is more palatable, but can cause problems if a producer feeds byproducts like corn gluten feed or dried distillers grains. The combination is too high in sulfur, which can cause its own set of problems.

Whatever the form, Lemenager recommends a mineral mix containing at least 8 percent to 10 percent magnesium. Cows should have access to the mix when grass starts to green up and the days begin to get warmer.

In Kentucky, Extension beef specialist Roy Burris specifically looks for a mineral that will supply around 22 grams of magnesium per head per day. “If the feed tag on the bag of minerals lists 14 to 15 percent magnesium, then the normal mineral consumption of four to five ounces a day will do that,” he says.

“I recommend putting out the high-mag mineral in January and leaving it out until the soil starts to warm up in April, depending on where you live.”

Changing your forage mix also can help.

“If you have legumes in your pastures, they also can reduce the potential for grass tetany,” adds Lemenager. “Those plants have a little different metabolism.”

Unfortunately, even for conscientious producers like Georgia’s Miller, all the risk factors aren’t always present. In his case, he kept a high-mag mineral out from November through April. He lost his cows in mid-January, which isn’t even close to spring in Georgia.

So the environmental conditions didn’t point to grass tetany as an immediate threat, but the animals themselves were prime candidates. All were 5 years old and at peak lactation, and Miller’s fescue pastures were lush.

“The only thing I can think of is we weren’t putting out any hay,” says Miller. “We were short on hay and we stopped feeding it because we had plenty of grass. This year, we’ll keep that hay out to hopefully dilute the effects of the grass.” — DTN