Corn harvest is in full swing in eastern Colorado, and livestock producers are making plans to
utilize those harvested acres. There are some considerations producers need to keep in mind before
turning out on corn stalks. Possible forage toxicity, fencing, water sources and forage availability should
all be considered in the planning for grazing corn stalks.
The first consideration is any possible toxicity issues with the corn stalks, specifically nitrates.
Nitrates are a major issue in corn plants that may have been stressed at the end of their growing season.
Nitrate levels above 5000 ppm can be toxic to cattle and over 10,000 ppm can be lethal. Testing the stalk
and leaf, the parts of the plant that can harbor toxic levels of nitrate, can give a producer a good
indication of whether to utilize a field or not. A simple diphenylamine test of sample plant material,
which can be done in the field or at your local Extension office, can indicate if nitrate levels are above or
below the toxic level. Any samples that have significant portions turn purple using the diphenylamine
test should be sent into a certified lab for further testing to find the level of nitrates in the samples. High
nitrate corn stalks can still be grazed if cattle are supplemented with low nitrate hay or concentrate feeds,
but it should only be done when the nitrate level of all forage and supplements is known and calculated
to be below the toxic level.
Providing water is the next consideration. Most grain fields do not have year-round water
sources developed. Temporary water sources are installed to meet the daily needs of the cattle. Daily
water needs are based on the size of cattle and the average ambient temperature.
If mature cows are being wintered on corn stalks they may need as little as 6 gallons per day
when temperatures are 40°F or less, but as much as 10 gallons during those warmer early fall days with
temperatures in the 70s.
Producers using round stock tanks for water should consider what type of cattle are using the
tanks. Mature cows may be able to reach the bottom of the tank and drain all water available in the tank,
but stockers and calves can only drink the tank down so far and then not be able to utilize all the water
available.
Choosing a grazing system is another consideration. A producer may choose to turn out on an
undivided field of cornstalks or using more electrical fence, divide and rotationally graze the field. There
are advantages and disadvantages to both. Utilizing an entire field at once is the least labor intensive but
tends to lead to declining TDN over the time of grazing as cattle forage the most palatable dropped corn
grain first, then leaves and finally cobs and stalks. Conversely, rotating cattle on a divided field is more
labor intensive, but cattle maintain a more level plain of nutrition as they move to new areas and go
through the forage palatability progression multiple times.
Calculating the forage available is usually a producer’s main consideration. The University of
Nebraska, Lincoln has done research and developed a simple formula to estimate grazing days per acre
based on the yield of the harvested corn. Using a 1200 pound non-lactating cow as the base animal, a
producer can take the corn yield in bushels per acre and divide by 3.5. For example, a corn field that
yields 200 bushels per acre, a producer could estimate 57 grazing days per acre (200 bu./ac. ÷ 3.5 =
57.14 grazing days). If a quarter section circle of corn (approximately 125 acres) averages the 200
bu./ac. yield, 7,125 grazing days is available (125 acres x 57 grazing days = 7,125 total days). A
producer who wants to use this field for 180 days could then estimate running 39 head of 1200 pound
cows (7,125 grazing days ÷ 180 days = 39.58 head).
Planning with these considerations in mind should help a producer to fully utilize acres of corn
stalks. There are still some other factors that can cause changes in usage, especially weather conditions,
but producers will need to be prepared to be flexible and adaptable to conditions they cannot control
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