If your silage corn was drought-stressed, frequently test for moisture content, starch content, and NDF digestibility. That way you can better formulate rations for high-producing dairy cows, says Ken Griswold, Pennsylvania State University dairy Extension educator for Lancaster County.
Drought-stressed corn is highly variable, which means its dry matter content within the silo – and when fed – will also fluctuate. So Griswold recommends testing corn silage's moisture content frequently. "Adjust as-fed feeding rates to maintain the correct dry matter amounts and proportions of silage in the diet," he says.
Expect the silage's starch content to be inconsistent, too. Because starch normally accounts for 65-70% of the energy content of corn silage, its content should be tested frequently and the diet reformulated to adjust grain feeding rates accordingly.
The overall energy content of the corn silage may not be dramatically lower, Griswold warns. During drought-stress, when ear development may be compromised, the plant will concentrate more sugars and organic acids in the stalk. Neutral detergent fiber digestibility (NDFD) may actually increase in drought-stressed corn silage compared to "normal" corn silage. If corn was too dry (<60% moisture) at harvest, however, the silage's NDFD may be lower than normal. So test NDFD on a more frequent basis, too.
Finally, silage made from severely drought-stressed corn should be tested for mycotoxins and nitrates. If corn was stressed during pollination and ear development, the silk ends of ears may have been open during kernel-fill, making them more susceptible to mold growth and mycotoxin development. If the corn silage has significant levels of mycotoxins, dilute affected silage with other forages or feed a mycotoxin binding agent.
Nitrate accumulation in drought-stressed corn is often highest for the first two weeks after a drought ends. Significant rainfall that fully moistens the soil will stimulate its microbes and cause a release of nitrate nitrogen. Corn plants recovering from drought will then take up large amounts of nitrate but be unable to fully assimilate it. As a result, nitrate will accumulate mainly in the lower part of the plant's stalk and it may take several weeks to be fully assimilated. Ensiling drought-stressed corn will cut nitrate levels in corn silage up to 50-60%, but it is difficult to predict how much of the nitrate will be broken down during fermentation and storage.
Test drought-stressed corn silage for nitrate content. If it has significant nitrate levels, dilute it with other low-nitrate feeds or don't feed it at all.
Click here for guidelines for feeding forages based on nitrate-nitrogen and nitrate concentrations.