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Little risk to grazing beef cattle on drought-stressed corn stalks
Harvest is here and the drought appears to be behind us for much of the Midwest. Fall rains have brought on some rejuvenation of pastures, but winter forage supplies are still low for many beef producers. With all the concern over nitrate toxicity, one of our most plentiful forage resources may be under-utilized. More than ever, beef producers need to utilize grazing corn stalk residues to save what little but valuable hay they may have.

Many veterinarians and nutritionists have fielded a lot of questions this year about nitrate toxicity. It is true that drought-stressed corn plants accumulate nitrates, but how much risk is there to your cow herd grazing corn stalk residues?

Nitrates accumulate in the bottom one third of the stalk. When cows are turned out onto a freshly-harvested cornfield, they will first eat any ears and shelled corn left behind. They will then seek out the leaves and husks and next the upper portion of the stalk and cobs. The last thing they will consume is the unpalatable bottom one third of the stalk where nitrates may have accumulated. Removing cows from the stalks when the upper portions of the stalks have been grazed and not forcing them to eat the bottom of the stalk will minimize the risk of nitrate toxicity.

More of a concern this year is cows getting too much grain when first turned out onto stalk fields resulting in rumen acidosis. The drought resulted in weaker stalks than normal and more down corn and dropped ears. It is important to walk your fields and know how much corn is out there. If it is a small area, it would be wise to pick up what ears you can. If there is too much corn out there to pick it up by hand, cows will need to be slowly adjusted to a high corn diet before being turned out on stalks. Stepping cows up with shelled corn until they are consuming 20 pounds per head per day will adapt their rumens to a high-starch diet. 

Also feeding a free-choice mineral that contains Rumensin will decrease the risk of acidosis problems. Feeding Rumensin at 200 milligram per head per day to beef cows will shift the bacterial population of the rumen to allow them to better utilize the corn. It also causes beef cows to eat smaller, more frequent meals thus reducing the risks of rumen acidosis. 

If you have access to corn stalk residues for you cow herd, they are still a valuable and plentiful forage resource following a drought. Nutrient levels are highest immediately following harvest, so it is important to utilize them soon. Don’t let concerns over nitrate toxicity cause you to not take advantage of grazing corn stalk residues.

D.J. Weimer, D.V.M.
Livestock Veterinary Services
Knightstown, Ind.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for D.J. Weimer may write to him in care of this publication.
10/18/2012