Got nitrates?

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.

Practice good feed management

If test results show worrisome nitrate levels in your corn silage, work with your nutritionist to adjust the ration accordingly. Here is some advice:

• LIMIT INCLUSION LEVELS. The amount of silage you should be able to feed depends upon the silage’s nitrate content and what animals you plan to feed it to. (For recommendations, please see “Is my silage safe to feed?” below.)

• GRADUALLY INTRODUCE THE SILAGE. Feed small amounts to start with and gradually increase levels over time.

• DILUTE IT. If possible, supplement with other forages to dilute the problematic silage. Work with your nutritionist on options that could work on your farm.

• CONSIDER ALTERNATIVES. Another option is to replace some of the corn silage with non-forage fiber sources. Some effective fiber is necessary in the diet, says Tamilee Nennich, assistant professor and extension dairy specialist at Purdue University. However, certain non-fiber feed sources, such as soybean hulls, corn gluten feed, cottonseed hulls and wheat midds, can help meet the cow’s fiber requirement. Straw or low-quality hay also may be an option.

Remember to consult with your nutritionist prior to altering the ration in any way.

Sampling drought-stressed silage

Proper sampling and analysis can help you make the most of drought-stressed corn silage harboring higher-than-normal nitrate levels. Here’s what you can do:

First, be safe. Do not take samples from the silage face because of both safety reasons and the inability to get a good sample, says Bill Weiss, professor and dairy extension specialist at The Ohio State University. Instead, take a few handfuls from several loader buckets over the course of a couple of mixer loads.

Put the handfuls into a 5-gallon bucket, mix well and dump the contents onto a clean floor or piece of plastic. Spread them out into a pie shape and divide the pie into quarters. Choose one quarter at random and put the contents into a re-sealable plastic bag. Follow your lab’s procedures for sending in samples.

If you store silage in silo bags, take five or six handfuls from the face, put them into a bucket and repeat the directions above.

It’s a good idea to sample periodically during the feeding period as silage is removed and put into the mixer, Weiss says. He recommends taking three or four samples over a short period of time (i.e., a couple of weeks) and using the average of the results to formulate the ration.

Is my silage safe to feed?

The following table shows recommended feeding guidelines based on nitrate nitrogen levels in corn silage:

click image to zoom

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