April 23, 2009

By Lisa Munniksma, Managing Editor

Grass tetany, also called grass staggers or hypomagnesaemia, is a magnesium deficiency
Courtesy USDA/Steve Asmus

As warmer spring temperatures approach and grass begins growth in earnest, it’s easy to be tempted to put your cattle on pasture right away so they can graze on the lush forage.

Before you do so, Purdue Cooperative Extension beef nutrition specialist Ron Lemenager, Ph.D., encourages careful management to prevent grass tetany and bloat.

“Benjamin Franklin once said, ‘An ounce of prevention is worth a pound of cure,’ and that is sure the case with these two abnormalities that we often see in some of the beef-cow operations,” Lemenager says.

Grass Tetany
Grass tetany, also called grass staggers or hypomagnesaemia, is a magnesium deficiency that usually occurs during a transition from cloudy, overcast and drizzly days to warmer temperatures.

Early lactating cows are the most susceptible, with older cows even more so than those with their first or second calves.

Lemenager explains that when animals are deficient in magnesium, they become highly excitable, which presents a challenge not only from the animal’s perspective, but also from an animal-handling standpoint. Other symptoms, according to the University of Florida Institute of Food and Agricultural Sciences Extension, include nervousness, lack of coordination, muscular spasms, staggering and death.

“Grass tetany incidents tend to increase in soils with higher potassium and nitrogen levels,” Lemenager says. “These are soils where maybe a lot of manure has been applied, causing a mineral imbalance.

“If suspicious, have your soil tested and forage analyzed. Forage containing less than 0.2 percent magnesium, more than 3 percent potassium and more than 4 percent nitrogen are likely to create grass tetany problems.”

Lemenager recommends feeding a magnesium supplement, such as a feed with 8- to 10-percent magnesium, during this period of increased risk. Supplements include magnesium oxide, which should be mix with molasses to make it more palatable; magnesium sulfate, although this can have negative effects if fed with corn gluten or dried distillers grains.

Animals that have experienced grass tetany are more prone to grass tetany in the future, so it’s important to keep good records on your animals’ health.

Pasture Bloat
An unrelated challenge of spring forage is pasture bloat, often called frothy bloat, a condition in which an animal is unable to get rid of gas produced as a normal part of rumen fermentation.

Pastures that are a 50/50 mix of legume and grass can help prevent both grass tetany and pasture bloat, Lemenager says. Planting birdsfoot trefoil—one of the non-bloating legumes—when renovating pastures can also help.

“Because bloat is more of a problem with legume pastures, particularly alfalfa and clover, it’s important to make sure the animals are full when you turn them out to pasture,” he says. “Even feeding a couple pounds of grain will help.

“It’s best to not send cattle out on wet pastures. Make sure the dew is off or, if it just rained, make sure it has dried up before you put the animals out—dry forage is better than wet forage.”

When rotating cattle to new pasture, time pasture rotation so there’s still forage left in the old pasture and so that animals aren’t hungry going to the new pasture. That’s good pasture management as well as good animal husbandry.

An anti-bloat agent such as Poloxalene can be fed three days to a week before cattle go to fresh pasture, and then when the animal is most susceptible to bloat. The antibiotic Rumensin also has some value in minimizing bloat.

Producers also need to make sure their animals are getting enough nutrients to meet their requirements. While the grass is greening up and growing rapidly, it contains a lot of water, Lemenager says. “This means the nutrients are diluted, which can create some challenges from the animal’s ability to eat enough to meet their nutritional requirements.”

If you suspect any of your cattle are prone to or experiencing grass tetany or pasture bloat, contact your veterinarian for guidance.

For more information about these conditions, click here.


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