If you have silage from a drought-stressed corn crop, you don't have to feed less of it, says Mike Hutjens.
“Producers who have large inventories of drought-stressed corn silage should try to build as much of it into their rations as they can,” advises Hutjens, University of Illinois extension dairy nutritionist.
When corn is grown and harvested under better conditions than Mother Nature provided this year, he says up to 75% of the forage in dairy rations can be corn silage. He's not backing down from that recommendation for drought-stressed silage, provided it's analyzed and rations are adjusted accordingly.
Droughty corn silage probably is below normal in starch content and fiber digestibility.
“Normal corn silage is high in TDN — usually testing in the low 70s,” says Hutjens. “The TDN of drought-stressed corn silage can be anywhere from 10% to 30% lower. That's our best estimate at this stage of the game.”
Ration changes may be needed to increase the energy level. “Those changes might include adding a couple more pounds of shelled corn to make the drought-stressed silage function the same as normal silage or adding soybean hulls for more fiber digestibility,” says Hutjens.
He recommends having the silage analyzed frequently — more often than usual — for moisture, starch, ADF, NDF and NDF digestibility.
“Because this year's corn crop is all over the map, corn silage is likely to vary not only from field to field, but also within the same field,” he says. “I was in a cornfield recently that was 5' tall with modest ears. Normally that corn would be 12' tall with big ears. That grower's ear-to-stalk ratio will actually be above normal because of the smaller amount of stalk dry matter.”
He also would have the silage tested for nitrates and mycotoxins.
“Anytime you have drought-stressed corn, there's a higher risk of nitrates and mycotoxins, including aflatoxins,” he says.
Drought-stressed corn tends to be higher in nitrates because the plants were unable to make use of the nitrogen absorbed. During the ensiling process, 35-50% of the nitrates are converted to silo gas and expelled.
Producers should be concerned if their corn silage tests over 4,000 parts per million (ppm) nitrate (NO3) on a 100% dry matter basis, or over 1,000 ppm nitrate nitrogen (NO3N).
“If the silage is above those levels after fermentation, the best solution is to add low-nitrate feeds to the ration,” says Hutjens.
If forage tests indicate elevated levels of mycotoxins, consider these options:
“Dilute the mycotoxins below the levels that can lead to problems — aflatoxins in the total ration dry matter below 20 parts per billion (ppb) and the other mycotoxins below 500 ppb,” he says. “Adding a mycotoxin binding agent can also reduce their impact.”