It’s that time of year again and even with all the rain you may have received, forage toxicity issues are beginning to appear just to the west of Osage County. There have been a few cases recently which cattle have been found dead among the toxic forage and these cases have been predominantly Johnsongrass. These particular cases actually occurred before the recent cool temperatures and with the warmer temperatures soon to return, the potential for seeing this in our area should dramatically increase.

Producers that have Johnsongrass in the pasture or within reach of the fence line should consider testing for the toxins Nitrate and Prussic Acid (aka Cyanide). Johnsongrass is our usual suspect in this area because the stem (or lower stem) may contain the high levels of Nitrates, but the upper part of the plant is where the Prussic Acid will accumulate.

Often, the most concerning for potentially dangerous levels of one or both of these toxins is in the recent &/or lush regrowth Johnsongrass we find in fields that are cut for hay in the first part of the summer then used for grazing thereafter. In these fields, plants are usually past the first joint or two in the stem and Nitrates can bind easily while Prussic Acid is produced in the upper plant, the part the grazing bovine eats first. Nitrogen fertilization tends to increase the likelihood of Nitrate Toxicity, but is not well correlated at all with Prussic Acid accumulation which tends to be more associated with rapid onset of heat, high heat after a brief rain shower, and the seasonal occurrence of first frost.

The stress from high heat and rain showers followed by high heat are also known to cause accumulation of Nitrates in the stems.

Baling hay containing elevated levels of Nitrates is also a problem as the levels of Nitrates in cut forage for hay will not decline over time. Testing should be done before hay is cut. Random sampling from around the field is VERY important as toxic levels will likely change around the field.

It is also important to understand that the level associated with mortality in bovine is also well above the level at which pregnant female bovine may abort pregnancy. To determine this, a producer will need to submit a sample to OSU Extension Office for lab analysis which may take 3-5 days once submitted. The OSU Extension Office in Pawhuska has a rapid testing solution that we can test your forage for Nitrate Toxicity, but it is only conclusive for a high level and an actual amount of Nitrates cannot be known without submitting to lab. In either case, producers should bring in whole plants which were cut approx. 4 inches above the soil surface.

This office can also test for the presence of Prussic Acid. To do so, a producer will need to cut sample leaves from the upper part of the plants and immediately place into closed Ziploc type bag to contain the loss of the Cyanide gas. For this reason, cut hay can be baled up with Prussic Acid toxic forage if well cured before baling. A hay swather which runs the forage through a set of rollers/conditioners is highly suggested.

OSU Lab fee for Nitrate Toxicity testing is $6/sample. Both the rapid tests for Nitrate testing and Prussic Acid are no cost to the producer as a service of this county office. The testing compounds are themselves harmful to humans so testing will be conducted by office staff only.

For any questions regarding testing potentially toxic forage, contact Will Cubbage, OSU Extension Ag Educator at 918-287-4170 or