Cows grazing cornstalks, it’s a common practice in the Midwest, albeit some information is being written about it as though it was a new practice. It isn’t. However much has been learned with more recent research data and the ability to efficiently utilize this resource has improved with different strategies. This season, with the drought conditions plaguing a large area of beef cattle production, grazing not only cornstalks but other crop residue will have a new value component.
What’s in the Residue?
Corn Residue or Cornstalks do provide an abundant source of forage. In Nebraska and other states of the Western Corn belt, it’s been called our winter pasture. Corn residue is composed of the husk, leaf, stem, and cob and waste grain left in the field after harvesting. The stem or stalk portion of the residue comprises nearly 40% of the dry matter, while the leaf and husk comprise about 45%, and cob about 10-15%. All of these components will vary in nutritional quality and digestibility and most attention should be given to the husk and leaf portion; which is what will provide the majority of the diet based on grazing management and diet selection of the animal. Thus, husk and leaf is about 60% digestible (based on in-vitro dry matter digestibility data) and will average about 3.5 -7.5% crude protein. Comparatively, cornstalk grazing is similar in quality as moderate to low quality hay.
What’s Grazed and When?
Most cornstalk grazing management recommends a 50% removal of the residue. When cattle are first turned into fields for grazing, they seek out waste corn first, then the husk and leaves. The stalks are normally the last components to be grazed and are lowest in quality. The amount of waste corn is variable due to harvest efficiency, ear drop caused by weather damage or other factors. A general rule is the amount of waste corn will average near 4% of the total dry matter available. If a great deal of waste corn is present (more than 8-10 bushel/acre) the risk of acidosis may be a concern, especially if the stocking rate is low. Having some waste corn in the residue does improve overall diet quality and digestibility, but this quality disappears quickly over time and is hastened by stocking rate. The diagram below illustrates this decrease in in-vitro dry matter digestibility as grazing days prolong.
Determining Stocking Rate
Appropriate stocking rate is related to the corn grain yield. A general rule is that 175 bushel per acre corn yield would supply about 1.5 AUM/acre of grazing; about 45 days of grazing for a 1200 lb. cow.  Grazing at 1 AUM per acre would be considered a light stocking rate and 2 AUM would be considered heavy. There is a free spreadsheet named “Corn Stalk Calculator” available through the University of Nebraska Extension Service. This spreadsheet can help calculate stocking rate, days of grazing, and total grazing cost. It can be found at www.unl.beef.edu. This is very handy to use and would be a good guide this year as corn yields under 175 bushel per acre are more common with the drought. Past stocking rates will probably not be a good guideline this season.
When evaluating the protein and digestibility values of various corn residue components, a convincing argument can be made for supplementation, especially protein. Quality of cornstalk grazing will be determined by stocking rate. The higher the stocking rate the faster the “goody” found in cornstalk grazing will be used up. Thus, the longer cows are grazed cornstalks in the same field, the lower the quality of their diet. There have been recent and ongoing studies evaluating the need for supplementation with cornstalk grazing. It would appear that with appropriate stocking rates, minimal weather challenges and a not so demanding stage of animal production ( 2nd trimester of gestation), mature beef cows would maintain Body Condition without protein or energy supplementation. I would caution the readers of that research to consider many things as it’s also shown that by supplementing on cornstalks, Body Condition can be gained. Mineral, vitamin and salt supplementation is also still necessary.
The 2012-2013 season is one where we will find many drought stressed cows and gaining a condition score in October, November and December will be a good thing, much better than just maintaining. In addition, with limited forage supplies, the use of cornstalk grazing or feeding cornstalks in many rations will be increased. As a cow-calf producer, one may be tempted to graze stalks a little longer or utilize more than the 50% recommended, simply due to the cost of forage. So with this in mind, supplementation is and will be warranted to best utilize the forage available. Crystalyx® has many good answers in products ranging from 20-40% crude protein. Consider these, and ones with a small portion of the protein from non-protein nitrogen (urea) to best utilize the fiber.
Nitrate, Mycotoxin, and Acidosis Concerns
Nitrates have been a concern in drought stressed corn. The good news is that most nitrate concentration in corn is found in the lower portion of the stem/stalk. Again, this would be the last component of the residue cattle would graze so avoiding nitrates is relatively easy with proper management and not over grazing. Similarly, with mycotoxins, the concern is in the corn grain fraction which, in most cornstalk grazing, is not a significant portion of the diet. Again, if more that 8-10 bushels per acre are determined to be wasted, acidosis may be a concern. In this case, management can help by cleaning up spilled areas of corn grain, strip grazing cornstalks (if practical), or simply increasing the stocking rate which removes the corn grain sooner and by a larger number of animals.
Cost of Cornstalk Grazing?
The numbers are all over the board. Here in Western Nebraska, the rates may have doubled in the last two years. Crop and hay values, coupled with drought and limited forage, have driven this. Cornstalks may not be the bargain they once were but still are a good value; even at $25.00 an acre, which is the asking price in many areas, it’s less than many summer grazing rates. Again, this number will vary from free for “Aunt Betty’s north quarter”, to as high as $50 or more by some exaggeration of coffee shop talk. What it is worth, is what’s paid for it. Thank goodness we have some cornstalk grazing this year
 Calculation based on 175 bushel per acre yield = approx. 16 lbs. of residue material, 50% of which is available for grazing. 50% X (16X175) = 1400 lbs. of DM available. A 1000 lb. cow = 1 AUM and requires 780 lbs. of DM/month. 1200 lb. cow = 1.2 AUM or 936 lbs. of DM/month. (1400)/ (1.2 X 780) = 1.50 AUM.