Jason Warner, cow-calf specialist
Each year, utilization of corn or grain sorghum residues following harvest by beef cattle represents an excellent opportunity to extend the grazing season into the winter thereby reducing the need to feed harvested forages. This year, for various reasons, there have been reports across the state of downed grain in residue fields at levels greater than typically seen. While it does require us to change our management approach, residue fields with high levels of grain on the surface of the field can still be grazed safely and economically. The degree to which grain in the field poses a risk is dependent on many factors, but if you are faced with determining how to best use a field that has downed grain, keep the following things in mind.
Type of Grain and Degree of Attachment to the Plant
The grain sorghum or milo kernel has a very hard outer coating and it also has a slower rate and lower extent of digestion than corn. Thus, the relative level of risk of acidosis or founder is lower for grain sorghum compared to corn. In order for the starch in either grain to be fully available to the microbes in the rumen, the kernels must be cracked or processed. While the rumination, or “cud chewing”, activity allows this to happen, the process of starch digestion is generally slower when the animal masticates the grain to break the kernel and is also consuming some forage from the plant at the same time. So, situations in which there are piles of loose grain on the field surface if the truck was overfilled or when cows unintendedly have access to grain that flows out of a silo bag at the edge of the field pose a much greater risk of animal losses than corn grain still in the ear or milo still attached to the head.
How Much is A Lot?
A sound estimate of the amount of grain down on the field surface can be challenging to assess, but it is very important. A field with 10 bushels per acre down is a much different situation than one with 75 bushels per acre on the field. In general, levels greater than 10 to 15 bushels per acre require additional caution and management. Estimates from yield maps in the combine can be helpful to identify areas in the field of concern. A simple method from colleagues at the University of Nebraska for determining the amount of downed corn is to measure out 3 different 100’ long strips in the field, add up the number of 8” ear equivalents and divide the number of ears by 2 to get approximate bushels per acre. For example, if strip 1 contained 4 – 8” ear equivalents, strip 2 contained 2.5 – 8” ear equivalents, and strip 3 contained 1.5 – 8” ear equivalents, then it would equate to 4 bushels per acre (4 + 2.5 + 1.5 ÷ 2).
Cattle Experience Matters
There are research data that suggest grazing is a learned behavior. Beef cows that have previously grazed crop residues will seek out and consume any grain present first before the husk, leaf, and stalk material. Heavily grazing (i.e. flash or mop grazing) fields with high amounts of downed grain with naive animals such as weaned calves first before turning in more experienced cows can be a method to lessen the risk to those animals. Likewise, consider grazing cull cows or bulls ahead of pregnant cows and heifers.
Animal and Field Management
Consider strip grazing fields with more than 10 to 15 bushels per acre rather than allowing access to the entire field. While this does increase the need for fence material and labor to move the fence, it does reduce the risk of acidosis/founder because the increased stocking density reduces grazing selectivity. Fill animals up with hay prior to turning them into the field to avoid them being hungry and grazing aggressively upon turnout. Consider supplementing grain, starting at 0.25% and gradually increasing up to 0.5% of BW, for at least 10-14 days prior to grazing high risk fields to help animals adapt to grain they will encounter during grazing. Supplementing a palatable source of hay to cattle while grazing high risk fields can help offset risk by substituting grain intake. Protein supplementation, particularly with a source of non-protein nitrogen such as urea or biuret, as well as providing an ionophore are both sound management strategies to improve cattle utilization of crop residue fields with excess downed grain.