With the frost that hit the region in recent days, the potential for prussic acid poisoning in livestock is likely on the mind of many producers. But, in addition to taking measures to prevent livestock toxicity, producers can also consider testing forage for prussic acid content, according to a forage expert with Ohio State University’s College of Food, Agricultural, and Environmental Sciences.
Some forage species, such as sudangrass, sudangrass hybrids, forage sorghums or sorghum-sudangrass crosses, can become toxic to livestock after a frost, said Mark Sulc, an Ohio State University Extension specialist. OSU Extension is the outreach arm of the college.
While producers can take steps to prevent or lower the risk of prussic acid poisoning in livestock, if they are still concerned that the potential is there, they can test the forage for its prussic acid content before feeding it to their livestock.
“Because prussic acid is a gas, producers need to be aware that it can be difficult to detect in samples by the time they arrive at the lab,” Sulc said. “Therefore, correct sample handling by producers is extremely critical to make sure that the lab results represent the condition of the forage that is actually being fed to livestock at the farm and that the prussic acid did not volatilize during shipment.”
In order to ensure accurate test results, producers need to get a fresh sample of one to two pounds of the forage from across the field to be grazed and store it in an airtight plastic bag before the sample has a chance to dry. The sample needs to be frozen quickly and shipped overnight in a cooler with an ice pack for testing.
“Producers need to be aware that because prussic acid dissipates with drying of the sample, if the sample arrives at the lab drier than the fresh forage that is fed, a false negative result will likely occur,” Sulc said. “It’s also a good idea to call the lab before you ship it to clarify sample handling procedures and so they will be expecting the sample.”
Some labs that test for prussic acid include: the Michigan State University Animal Health laboratory, which can be found here and the Cumberland Valley Analytical Services, Inc., which can be found here.
While prussic acid is extremely poisonous, cases of livestock poisoning are fairly uncommon, Sulc said, because most producers take measures to reduce the potential.
Some steps producers can take to reduce prussic acid poisoning include avoiding grazing on nights when frost is likely; not grazing after a killing frost until plants are dry, which usually takes five to seven days; and avoiding grazing wilted plants or plants with young tillers, he said.
“Waiting a few days after frost then cutting and harvesting the forage for dry hay or baleage/silage also reduces the risk significantly,” Sulc said.