Fall frost can raise the potential for prussic acid poisoning in livestock, meaning producers need to properly manage forages and possibly test for prussic acid content, an Ohio State University Extension forage specialist says.

Prussic acid poisoning in livestock is potentially of broader concern this year because drought conditions left many livestock producers short on hay and silage and looking for alternative forages.

Many chose to grow sudangrass, sudangrass hybrids, forage sorghums or sorghum-sudangrass crosses, which are capable of becoming toxic to livestock after a frost event, Mark Sulc said.

Producers can take steps to reduce prussic acid poisoning, including: 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.

But for those who want extra reassurance that their forage is safe from prussic acid, they can have forage samples tested.

“If producers believe there is a high potential for toxicity, they should test the forage before feeding it to their livestock,” Sulc said.

To do so, producers need to get a fresh sample of one to two pounds of the forage 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.

“It’s a tricky test to do because the gas (prussic acid) dissipates quickly,” Sulc said. “So sample handling protocol and getting it quickly to the lab are critical to obtaining results that represent the condition of the forage that is actually being fed back at the farm.

“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.”

While prussic acid is extremely poisonous, Sulc said it’s an uncommon problem.

In fact, animal deaths from it are rare because most producers are very good about following the guidelines to prevent prussic acid poisoning, he said.

“People are aware of the danger when they get the first frost,” Sulc said. “They’ll call in and ask for information and review the guidelines for handling the danger.

“Overall, people are doing a really good job managing forages that are potentially dangerous to feed after a frost. It is just something that you have to be aware of because the potential is there, although it can be managed very effectively by following proper guidelines.”