Some forage species can develop prussic acid poisoning potential when harmed by frost and management practices should be followed to prevent poisoning of livestock (see accompanying article). If doubt remains regarding the safety of the forage, it can be tested for prussic acid (cyanide) content.
Keep in mind that prussic acid is a gas, so it is difficult to detect in samples sent to labs. Sample handling is extremely critical to ensure that the lab test will be representative of what is being fed to livestock and that the prussic acid did not volatilize during shipment.
Obtain a representative FRESH sample of the forage to be fed. Collect 1 to 2 lbs of fresh forage from across the field to be grazed. For silage, follow proper sampling protocol to obtain a representative sample.
Do not allow the sample to dry. Place in an air-tight plastic bag, freeze the sample quickly, and ship to the lab the fastest way (overnight express) in a cooler with an ice pack.
Remember, cyanide content dissipates with drying of the sample. So if the sample arrives at the lab drier than the fresh forage that is fed, a false negative result will likely occur.
The following are two labs that will analyze samples for prussic acid (cyanide). Other labs may provide testing for prussic acid, always call ahead to confirm whether the prussic acid test is provided and to ask them about their recommended sample handling protocols.