By Mike Jarosz, Ph.D.
Cornstalk residue has been a major forage resource, especially for cow/calf producers in the heavy farming areas of the United States. From 1990 to 2013 the amount of corn residue increased an estimated 105 million tons (Watson et al., 2015). Not only has the amount available changed over time, in general it appears the nutrient content of the corn stalk residue has changed as well.
Not all of the corn residual components are created equal in regards to the amount of each plant component in the field, the nutrient content of each, and what cattle prefer to consume. Cattle select first for the components highlighted in the box in Table 1 (the husks, leaf blade, and leaf sheath), where over 60% of the residue cattle would prefer not to consume. If they have experience with grazing corn stalks, they will commonly consume the corn grain that may be left in the field as a first priority, but with new hybrids, better equipment, etc. relatively little corn grains remain in the field.
Table 1. Proportion of plant components of corn residual and analyzed nutrient content of each (Adapted from Watson et al., 2015).
Since cattle prefer to only consume part of the corn residue, it is estimated for every bushel of corn yield, roughly 8 lb. of dry forage cattle would actually prefer to consume for each acre of corn. For a cornfield with a corn grain yield of 200 bushel/acre, it is estimated 1568 lb. of consumable forage is available that a cow would eat, so one acre of these corn stalks would support one 1300 lb. cow for about 60 days.
Since cattle are able to sort the corn stalk residue, the diet they select for is commonly better than sampling everything in a given area to ground level and analyzing. Wilson et al., 2004 measured the protein content and digestibility of what cattle consume and found it to be 6.5-7% crude protein (DM basis) and ~53%, which is part of the reason cattle seem to perform better grazing corn stalks than expected.
Another piece to be aware of is the quality of stalks appear to be changing over time. Table 2 compares what the Beef NRC had for 1984, NRC, 1996, and compared to the average of 3 stalk fields sampled in eastern Colorado in 2014. Crude protein (c. protein) and calcium (Ca) content are two nutrients that have been trending downward. The lower protein content meaning it may take additional protein supplementation to meet cattle requirements and by providing supplemental protein, it can lead to improved microbial growth and better forage digestibility. In regards to Ca, commonly forages have contained enough calcium to meet requirements especially for brood cows, but with corn stalks the Ca appears to be trending downward over time and is becoming more important to supplement.
Table 2. Beef NRC book values as compared to corn stalks sampled in Colorado in 2014.
The nutrient content may also vary from field to field, in Table 3 evaluating the protein and Ca levels between 3 different stalk fields, field A had lower levels than the other two fields. It is ideal to obtain samples of stalk fields to better verify nutrient levels, in general, the supplemental needs of cattle consuming corn stalks are likely higher than they were years previously. Work with your QLF representative to help analyze your specific situations and perform rations for the cattle grazing the corn stalks you have to make sure animal requirements are being met and balanced.
Table 3. Variation in nutrient content of different stalk fields in eastern Colorado.
NOTE: Fields sampled the same day within 3 miles of each other in eastern CO.
Watson, A. K., J. C. MacDonald, G. E Erickson, P. J. Kononoff, and T. J. Klopfenstein. Optimizing the use of fibrous residues in beef and dairy diets. J. Animal Science. 2015.
Nutrient Requirements of Beef Cattle. National Research Council. 1984
Nutrient Requirements of Beef Cattle. National Research Council. 1996.