April 21, 2009

Expert: Beware of grass tetany, pasture bloat in cattle

The recent temperature change from cold to warm in the Eastern Corn Belt has many beef producers anxious to turn their cattle out to pasture. But Ron Lemenager, Purdue Extension beef nutrition specialist, said it is important to manage herds 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 said.

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

Early lactating cows are the most susceptible, he said, with older cows considered more susceptible than those with their first or second calves. Older cows seem less capable of pulling magnesium reserves from their bones than younger cows, Lemenager said.

He said that when animals are deficient in magnesium they become highly excitable, which presents a safety issue for the animals and their handlers.

"Grass tetany incidents tend to increase in soils with higher potassium and nitrogen levels," Lemenager said. "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 recommended feeding a high-magnesium supplement during this period of increased risk. A feed tag with 8 percent to 10 percent magnesium content would be appropriate, he said.

"Magnesium oxide is a common supplemental form of magnesium, but it is bitter and unpalatable, so something like molasses needs to be added to make it palatable," he said. "Magnesium sulfate is another form, and it's more palatable, but can cause problems if a producer has been feeding byproducts such as corn gluten or dried distillers grains with solubles. This combination is too high in sulfur and can create additional problems."

Animals that have had grass tetany are more prone to grass tetany in the future, Lemenager said. Producers need to think about how they are going to manage an animal that has had grass tetany in the future - whether that means culling it from the herd, feeding it differently or keeping a closer eye on it, he said.

The second unrelated challenge producers face is pasture, or frothy, bloat. This condition prevents animals from expelling gas that is a normal part of rumen fermentation.

"The gas is not a free gas," he said. "It's actually entrapped in foam bubbles, and the animal can't get rid of it, which causes extreme discomfort and can suffocate the animal."

Pastures that are a 50/50 mix of legume and grass can help to prevent both grass tetany and pasture bloat, Lemenager said.

"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 said. "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."

He added that when rotating cattle to new pasture, make sure they are full on the old pasture before moving them. Time the rotation so that there is still forage left in the old pasture and the animals aren't hungry when moved to the new pasture.

Lemenager also said an antibloat agent such as Poloxalene can be fed (2-4 grams per 100 pounds of liveweight) and should be given three days to a week before cattle go to grass and during the time when it is most susceptible to bloat. Rumensin also has been shown to be of some value in minimizing bloat, he said.

Another management practice that can help is planting birdsfoot trefoil - one of the non-bloating legumes - when renovating pastures.

Producers also need to make sure their animals are getting enough nutrients because grass that is greening up and growing rapidly contains a lot of water.

"This means the nutrients are diluted, which can create some challenges to the animal's ability to eat enough to meet their nutritional requirements," Lemenager said.

"I can't stress prevention enough."

More information on grass tetany and pasture bloat is available online at https://www.ansc.purdue.edu/beef/  or by contacting Lemenager at 765-494-4817, rpl@purdue.edu

Writer: Julie Douglas, 765-496-1050, douglajk@purdue.edu

Source: Ron Lemenager, 765-494-4817, rpl@purdue.edu

Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
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