Producers with livestock grazing drought-stressed cornstalks are running into nitrate-toxicity problems, warns Dan Undersander, University of Wisconsin Extension forage agronomist.
They should test stalks for nitrates before grazing, especially in fields where forage and grain yields were reduced by more than 50%, he says. Nitrates are more concentrated in lower stalks than in leaves and upper stalks.
If a test comes back showing toxic nitrate levels, consider these options:
1) Wait to graze cornstalks. Because nitrates are soluble, some will wash out of leaves and stalk with rains greater than 1” - to an extent. Test forage again after a rain to determine remaining nitrate levels.
2) Dilute cornstalks with toxic levels with non-toxic feeds:
• Feed a supplement, such as corn. This not only reduces the nitrate concentration, it provides energy so the nitrite can be metabolized to some extent.
• Limit-feed cornstalks so animals will consume hay, other crop residue or silage to dilute nitrates in cornstalks.
“Knowing the nitrate level of the feedstuff is crucial before feeding to cattle. We tend to think of animal deaths from nitrate (nitrite, actually), and many will think if no animals died, they got by,” Undesander says.
But subclinical nitrite poisoning can also cause considerable damage to animals, including degeneration of the vascular tissues of the brain and other organs. Affected animals may appear to be healthy, but can abort their young, fail to settle to service, suffer a decline in lactation or not be able to adjust to cold temperatures, he points out.
Nitrates also decrease iodine uptake by animals’ thyroid glands, so Undersander recommends that producers have iodized salt bocks available to cattle grazing cornstalks.