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Avoid fall grazing illness

Justin Davey 10/23/2012 @ 4:41pm

With an extremely hot, dry summer behind us, cattle grazing practices may need to be tweaked to keep animals healthy. Many farmers have turned to letting cattle graze corn fodder as a cost-effective feedstuff, but without proper rumen adaptation to starch, they could suffer acute acidosis - a sudden drop in rumen pH caused by rapid grain overload that can lead to illness or death.

"In the more seriously stressed, lower-yielding fields, some producers are reporting ear drop resulting from stalk quality issues and 'nubbin' ears that are slipping through the stripper plates of the combine head," says Ron Lemenager, Purdue Extension animal scientist. "Collectively, this ear drop can create acute acidosis when grazing cornstalks if not managed correctly."

Part of acidosis management is to scout fields before turning out cattle to determine how much corn is there, Lemenger says. Producers could feed several pounds of corn grain per cow daily for several days before allowing them to graze, which helps adapt the rumen to starch.

Cattle also should be full of dry hay before turnout so they don't eat as many ears. They should be turned out midday to allow cornstalks to dry from morning dew. Dry forage stimulates saliva production and can provide a bit of a rumen buffer to help minimize a sudden pH drop.

"After several days, the rumens should be adapted to starch and the concern of acidosis is reduced."

Even when properly managing livestock grazing on cornstalks, Lemenager advised that producers should still know the symptoms of acute acidosis. Cattle at first will look stressed or gaunt and could stop eating. Further along, they could have loose, gray stools and eventually might have elongated hoof growth.

Also, now that cooler temperatures have returned, a springlike regrowth in pastures can present some additional health risks for grazing cattle. 

Lush growth in predominantly grass pastures can cause cattle to suffer grass tetany, a potentially fatal condition caused by a magnesium deficiency. Bloat, on the other hand is more of a concern in heavy-legume pastures.

"Generalities can be dangerous, but grass tetany is classically seen in the spring with older, lactating beef cows on lush, vegetative, grass pastures when nighttime temperatures are below 55 degrees," Lemenager says. "These are the same conditions our fall calving herds are now experiencing, which makes them the most susceptible."

With the lack of rain for most of the summer, grasses have reduced magnesium uptake from the soil that is aggravated when soil profiles are high in potassium and nitrogen. Many producers fertilized pastures in the spring, and with the drought, there has been some nitrogen and potassium carryover.

Grass tetany is especially dangerous because the time from the first symptoms to coma and death can be as few as two to three hours, he said. Symptoms include excitable and possibly aggressive behavior, muscle tremors, and convulsions.

Bloat is a digestive disorder caused by the accumulation of gas in the rumen. Gas production is a normal result of rumen fermentation, but when the animal's ability to release the gases is impaired, pressure builds and bloat happens.

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