Drought-stressed, nitrate-laden corn has caused cattle deaths in southern Wisconsin. That’s all the more reason producers should check nitrate levels of such forage before feeding it, warns Dan Undersander, University of Wisconsin Extension forage specialist.

“We had one report of 36 dying and another of 16 dying. When all or a large portion of a pen is dead, that’s oftentimes a pretty good indication that the cause was nitrate poisoning, because there isn’t much else that will kill a whole pen of cattle,” he says.

Nitrates can accumulate in stalks as lack of moisture limits plant growth. Once cattle consume such forage, nitrates turn into nitrites, which can bind to red blood cells, preventing them from carrying oxygen to tissues. Eventually, an animal will die from lack of oxygen.

The level of nitrate accumulation, however, depends on many factors, including the type of hybrid, when it’s planted, growth rate, how it’s harvested and how it’s fed, Undersander says.

For livestock producers trying to make use of droughty corn, the best option is to ensile it, wait two to three weeks until it has fermented, then check nitrate levels and feed accordingly.

“We really feel that feeding fresh corn, at this point, is very risky. Our first recommendation is to not greenchop any corn, but only make silage from it; test it and then feed the silage. The level of toxicity in fresh forage can change very quickly. For instance, with the rains we had, forage might take up a little more nitrogen and suddenly become toxic.”

Ensiling droughty corn removes from 10% to as much at 30-40% of the nitrates, he says. Once the corn has fermented, an entire lot of silage has similar nitrate levels and only needs to be tested once before feeding.

If feeding greenchop, however, producers should test that feed daily. Nitrates change quickly in fresh forage, so samples need to be sent to commercial labs within an hour or two or frozen immediately. That’s the only way producers can expect to get accurate readings, Undersander says. Ensiled samples don’t need such care.

Producers also should realize that nitrate reporting isn’t standardized and that some labs will report for nitrate, for example, and other labs for nitrate-nitrogen or some other measure. “The key thing is to understand that there is a difference and, when you get a report back from the lab, have it tell you what the toxic level is for their analysis.

“Once you find out what the nitrate level is in the forage, you could dilute your total ration appropriately, so that it’s no longer at a toxic level in the ration. For example, if your forage is at or somewhat above the toxic level, you might dilute it with 30-40% hay that isn’t nitrate-toxic,” he says.