Cow

Pasture and rangeland forage shortages have producers looking for other feeds to supply nutrients needed by their livestock. Additionally, many crops did not produce the same quality of products that can be marketed without discounts. Hence, some producers are considering grazing standing corn that has been affected by moisture shortages, hail, wind or a combination of factors.

Corn

Grazing standing corn has been done for years. However, if you are new to this option, there are a few factors that should be kept in mind.

If the field you are considering grazing is covered by crop insurance, first you will want to visit with your agent.

You need to confirm what chemicals — herbicides, pesticides, etc. — were applied to this crop and if they are approved on the label for grazing at this time.

If the field is stressed from drought, hail or some combination of these factors, test for nitrate levels. These stress factors reduce photosynthesis and the conversion of nitrates to plant proteins. The nitrate concentrations are normally higher in the bottom third of the plant.

Next, producers should estimate the amount of corn grain is present in the field. Count the ears for a given portion of an acre. When counting the number of ears, also evaluate the ears for damage and mold growth.

If the field has uniform growth, sampling at one sample for every 10 to 15 acres would be ideal. However, with large fields, this might not be practical. If the field is nonuniform, you will want more samples.

Multiply the average number of rows per ear by kernels per row by the number of ears in a thousandth of an acre and divide by 90 to estimate yield in bushels per acre. For example, 16 rows times 40 kernels times 32 ears equals 20,480 kernels in a thousandth of an acre divided by 90 equals 227.6 bushels per acre.

With 15-inch rows, use 17 feet and 5 inches and count the two adjacent rows.

Corn that is damaged or downed due to stalk rot, hail or other conditions may be prone to mold development. If extensive molds are present, testing for mycotoxins should be completed. It is important to understand that molds produce mycotoxins, but molds by themselves do not cause problems to animals. However, the mycotoxins molds produce can cause significant problems for livestock.

Livestock

The livestock side also has some important considerations to ensure that you are mitigating risks when grazing standing corn.

Animals should be adapted to corn prior to turnout to reduce digestive upsets or undesired conditions, such as lameness or abortions. Cattle should be worked up to seven to eight pounds of corn per day prior to moving cows to standing corn.

Start with approximately 2-3 pounds daily and add 1 pound every other day, and in a 10-day period, cows will be up to 7-8 pounds of cow per day. See Grain Overloads: A Possible Consequence of Cornstalk Grazing for more information.

Selection of which class of cattle will be allowed to graze is another question. Naïve animals will take longer to find the ears. However, cows that have grazed corn residue or standing corn will target the ears immediately. If a high amount of grain is present, consider using yearlings, calves or cull cows prior to the pregnant cows.

Strip grazing standing corn limits access to the entire field, hence limiting corn intake. Ideally, you would want to provide a one-day supply at a time. However, to be practical, many producers would limit the area to two to three days worth of feed.

The normal rule of thumb is when you don’t see corn kernels in the manure, consider adding a protein supplement. However, when grazing standing corn during a drought situation and corn kernels are not seen in the manure, move cattle to new areas. The lack of corn kernels may indicate that they are having to consume more of the stack — normally higher in nitrates.

Molds, mycotoxins

Molds, such as Aspergillus, Gibberella, Fusarium and Diplodia, may be an issue. The mycotoxins with higher prevalence are Aflatoxin; Ergot/Scab, which causes high levels of Zearalenone, DON/Vomitoxin, Fumonisins and T-2 toxins, which may occur here, but less frequently and shouldn’t be ruled out.

The effects of mycotoxins on beef cattle can be quite vague and may not occur until long after the impacted feed is consumed, making diagnosis difficult. Some potential effects include reproductive problems (due to zearalenone or aflatoxin), decreased milk production, poor health and suppression of the immune system (aflatoxin) and digestive problems (T-2). For more information, see the article, Can Livestock Utilize Moldy Grain?.

Feed testing

Producers wishing to have their grain or feed tested to be used in animal feeding operations can send samples to either the SDSU Plant Diagnostic Clinic in Brookings, South Dakota or the NDSU Veterinary Diagnostic Laboratory in Fargo, North Dakota.

If mycotoxins are detected, producers should consult their veterinarian or nutritionist.

Depending upon the type of livestock, it may be advisable to avoid grazing if high levels of mycotoxins are demonstrated.

Grazing standing corn is a viable option to supply nutrients to livestock. However, mitigating risk is critical to ensure healthy animals and optimize crops.

Julie Walker is a professor and South Dakota State University Extension beef specialist.

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