Numerous corn and sorghum samples have tested positive for high levels of nitrate and prussic acid. Forages containing high levels of either compound are potentially lethal when grazed or fed as hay to livestock, according to a Texas AgriLife Extension Service expert.
“Agricultural producers can follow several steps to minimize nitrates in the baled forages, including raising the cutter height to leave the high-nitrate lower stalk in the field,” said Dr. Tony Provin, AgriLife Extension soil chemist and director of the Soil, Water and Forage Testing Laboratory  in College Station.
Since nitrate accumulation and prussic acid occur in different parts of the plant, Provin said, it’s difficult for one sample to detect both potential threats.
“Producers should sample multiple plants and segregate the lower portion of the stalks for nitrate analysis,” he said.
Samples between 8 inches and 16 inches will help reveal concentrations at different heights, allowing the producer to adjust cutting equipment accordingly and minimize nitrates baled in the hay.
“While nitrate levels are highest in these lower stalks, a producer may elect to measure nitrate concentrations in the remaining plant to provide added assurance that it is safe for grazing, in the event the lower 16 inches of the stalk (often considered the highest a cutter bar can be raised) is highly elevated with regard to nitrates,” Provin said.
Meanwhile, prussic acid only occurs in a select number of crops and weeds, he said. Producers should pay special attention to sudangrass, sorghum, and johnsongrass.
“For these species, prussic acid can form in the newest leaves or recently damaged leaves,” he said. “Samples collected for prussic acid analysis should be comprised of the newest leaves and damaged leaves.”
The Texas A&M System Texas Veterinary Medical Diagnostic Laboratory  can provide further information on the sampling and testing of these samples.
Tight bales may require more than nine months for prussic acid levels to decline below levels of concern, he said. Good field curing of hay, specifically aided by the utilizing crimper/conditioners, usually reduces the threat to more negligible levels.
“Nitrate levels will remain constant unless significant water leaches through the bale, a factor often reducing the feeding value of the hay to near zero,” Provin said.
A publication is available for download at the AgriLife Extension bookstore  that provides complete background and sampling instructions.