Eight farmers brought corn stalks to a meeting to have them tested for nitrates so they could determine if levels of the compound were safe to feed to their cattle. Nitrate levels in six of the eight samples were too high. Sound familiar?
As of mid-August, nearly 90 percent of the nation’s corn crop was impacted by drought, with more than half in extreme to exceptional drought. That means there will be a lot of drought-damaged corn being fed as silage. And with that comes the threat of increased nitrate levels, which you know can be dangerous, even deadly, for dairy cows.
Here are some recommendations for preventing nitrate toxicity when feeding corn silage harvested from drought-damaged fields.
Let it ferment
Certain harvesting strategies, like raising the cutting height to avoid chopping the bottom of the stalk where nitrates accumulate, go a long way toward reducing nitrate levels. The silage fermentation process also works in your favor.
“Nitrate concentrations are often reduced during silage fermentation so that high nitrates in fresh corn plants may end up as acceptable concentrations in the fermented corn silage,” says Bill Weiss, professor and dairy extension specialist at The Ohio State University.
Estimates vary, but generally you can expect fermentation to reduce nitrate levels in drought-damaged corn silage by at least 25 percent or more. The use of inoculants that improve fermentation might even bump that up a little more.
A good rule-of-thumb is to let the silage ferment for at least three to four weeks post-ensiling before you feed it.
Test, test, test
Even if you did everything “right” during harvest and ensiling, you should still have the silage analyzed for nitrates, in addition to its nutrient composition, before feeding it.
When you do this, take a few more samples than you normally would because drought damage can increase nutrient variation between samples.
“Sample-to-sample variation is probably much higher with drought-stressed corn because field growing conditions would be more variable,” Weiss explains. “Some plants will be severely stunted, while others may not.”
Taking three or four samples should be sufficient, Weiss says.
Obviously, nutrient variation can be problematic during ration formulation, so when you get the results back, take the average and use that during diet formulation.
Generally, drought-damaged corn silage has a pretty good feeding value, unless it’s extremely damaged. So, for the most part, you can still use the same ration specs, Weiss says, but you may need to supplement more corn grain or another starch source in the diet.