“Due to variability in stalk and ear development, corn silage made from drought-stressed corn should be tested more frequently for moisture content, starch content and NDF digestibility in order to better formulate rations for high-producing dairy cows.”
That’s advice from Ken Griswold, dairy Extension educator in Lancaster County, PA, who points out that the 2010 corn crop in his state was subjected to drought stress, especially early planted, short-season hybrids. If the corn plant was in tassel and going through pollination when the heat and dry weather was most severe, the plant was likely shorter than normal with smaller ears that may have had aborted kernels and poor kernel fill, he says. If the drought stress occurred prior to pollination, the plant would be shorter than normal, but may have had fully developed ears.
A number of issues must be considered when feeding the drought-stressed crop, says Griswold. First, the silage within the silo probably has wider swings in dry matter content. Therefore, it should be tested for moisture content more frequently at feed-out to adjust as-fed feeding rates to maintain the correct dry matter amounts and proportions of silage in the diet.
The starch content is likely to be more variable, too. As starch normally accounts for 65-70% of the energy content of corn silage, it should be measured more frequently and the diet reformulated to adjust grain feeding rates accordingly.
The overall energy content of the silage may not be dramatically below normal, Griswold adds. When ear development is compromised, the plant concentrates more sugars and organic acids in the stalk. Further, neutral detergent fiber digestibility (NDFD) may be higher than normal. However, if the corn was too dry (less than 60% moisture) at harvest, the silage NDFD may be low. Therefore, NDFD should be tested on a more frequent basis to more accurately estimate the energy content of the corn silage.
Finally, if you made corn silage from severely drought-stressed corn, it should be tested for mycotoxins and nitrates. If pollination and ear development were occurring during the dry period, the silk end of the ear may have been more susceptible to opening during kernel-fill. Open-ended ears may be more susceptible to mold growth, which may provide an opportunity for mycotoxin development. If the silage has significant levels of mycotoxins, there are normally two options: dilute the silage with other forages or feed a mycotoxin-binding agent.
Nitrate accumulation is often highest for the first two weeks after a drought is ended by significant rainfall. Significant rainfall events that fully moisten the soil will stimulate the soil microbes and cause a release of nitrate nitrogen. The corn plants recovering from the drought will then take up large amounts of nitrate, but will not be able to fully assimilate the nitrate. As a result, the nitrate will accumulate in the plant, mainly in the lower part of the stalk. The plant may need several weeks to fully assimilate this nitrate accumulation. Ensiling drought-stressed corn reduces nitrate levels in the silage by up to 50-60%, but it’s difficult to predict how much of the nitrate will be broken down during fermentation and storage.
“Drought-stressed corn silage should be tested for nitrate content, and if it has significant nitrate levels, then the corn silage should be diluted with other low nitrate feeds or not fed at all,” says Griswold.