Prussic acid poisoning in forages
Be aware that there can be two separate but somewhat related toxicities: prussic acid and high nitrates. Both can occur in plants stressed by drought or frost. However, the toxicity principles and recommendations are much different.
In general both risk situations are a result of plant stress from environmental conditions, over-application of N fertilizer or manure and sometimes poor livestock management. We recommend testing for both nitrates and prussic acid if there is any of the predisposing conditions (separate tests but can be the same lab).
The high nitrate problem is usually greatest in the stems and high nitrates do not decrease with time or drying. High prussic acid usually declines with time (usually more than 5 days) and drying out. High prussic acid may be greatest in the leaves.