Grazing corn stalks is a common practice and typically one of the most cost effective ways to winter cows. Historically corn stalks have had a predictable feed value and could maintain body conditions (BC) on a bred cow with minimal supplementation. If managed correctly cows can gain BC while grazing stalks, however, over grazing and loss of BC is always a concern. Producers always want to get the most out of a field sometimes at the expense of BC.
Grain, husk and leaves are the most palatable and nutrient dense fractions left in the field. Stalks and cobs are the least palatable and least nutrient dense fractions and cows do a great job of foraging for the grain, husk and leaves when first introduced to a field leaving stalks and cobs for last. Husk and leaves make up about 40% (Wilson et al. 2004) of the dry matter of a stalk field. Therefore, the take 50 leave 50 is a good rule of thumb for grazing stalks. Once 50% of the fodder is removed by the cows what is left will not have the nutrients needed by a cow. Therefore cows must be moved or an increase in supplementation must occur to maintain BC.
Many producers have expressed concerns that corn stalks have a lower feed value today than they have in the past, and many of the corn stalk analysis I have seen seem to agree with that. Not only lower energy but also lower in calcium, magnesium and protein. National Research Council reported values for corn stalks in both their 1984 (this did not include husk) and 2000 publications. Values from the 1984 NRC were 50, 6.6, 0.57, 0.10 and 0.40; values for 2000 were 65.9, 6.5, 0.62, 0.09, and 0.00 (percent TDN, CP, Ca, P and Mg; respectively). Table one contains the analysis from 3 fields of corn stalks analyzed in 2014. It appears that concerns over nutrients decreasing in corn stalks are justified; also stalks seem to be more variable in their nutrient profile. The reduction in energy could be due to breeding plants with more lignin in the stalks making them stronger and less likely to fall and resulting less ear drop as well. Also breeds of corn may have a different ratio of husk and leaves to stalks and cobs. Better harvest equipment leaves less grain in the fields for the cows reducing the energy value of what is in the field. The change in Calcium and Magnesium are a little harder to explain but could be due to breeding or simple mining the soil of these minerals by not replacing them with fertilization. With all of this in mind supplementation has become more important than ever.
In many cases, NRC may over estimate nutrient value of corn stalks which will diminish cow performance. Table 2 demonstrates the gap that would need to be bridged by a supplement for a cow grazing an average of the stalk fields in table 1. To bridge the gap with a 2 lbs/hd/d supplement it would need to be 35% CP, 30% TDN, and 0.31% Phos. In stalk field 1 Ca supplementation would be needed as well. Alliance Liquid Feeds tries to be proactive; when a trend of declining Ca levels in stalks was noticed, Ca was added to bitter formula to help offset this trend. However, Ca levels in liquid supplement have to be limited for a number of reasons. Therefore, if feeding rates are restricted or if the base forage is significantly deficient another source of Ca must be fed. Properly sampling stalk fields for analysis is important part of managing feed resources and avoiding nutrient deficiencies that can cause production losses. If samples are not taken Alliance Liquid Feeds recommends that you assume a worst case scenario and feed additional Ca. Calcium mix with loose salt, alfalfa or a dry mineral with Ca and P are all good options to insure Ca is sufficient in the diet. For more information about supplementing strategies or for help balancing rations please contact Technical services.
Table 1. Corn stalk analysis for winter of 2014 (DM basis)
|Items||Stalk Field 1||Stalk Field 2||Stalk Field 3||2001 NRC|
|Crude Protein, %||3.8||5.4||5.5||6.5|
Table 2. Gap between the requirement and nutrients provided by base forage for a 1300 lbs cow -Last Trimester
|Items||Requirement||Average of Stalks||Difference|
|Stalks, lbs DM||26|
|Crude Protein, lbs/hd/d||2.0||1.3||-0.7|
NRC. 2000. Nutrient Requirements of Beef Cattle. Seventh Revised Edition. National Academy Press. Washington, DC.
NRC. 1984. Nutrient Requirements of Beef Cattle. Sixth Revised Edition. National Academy Press. Washington, DC.
Wilson, C. B., G. E. Erickson, T. J. Klopfenstein, R. J. Rasby, D. C. Adams, and I. G. Rush. 2004. A review of corn stalk grazing on animal performance and crop yield. Nebraska Beef Cattle Reports 2004:13-15.