Source: University of Missouri Extension
Many landowners have had questions about the risk of grazing or haying johnsongrass or sorghum sudan forage.
The exceptionally dry weather has placed a lot of stress on the plants and increased the risk of prussic acid and/or nitrate poisoning according to Eldon Cole, livestock specialist with University of Missouri Extension.
"The principal causes of this risk are different but some plants may exhibit a risk for both. As other forages dry up, these more dry-weather tolerant plants can become the most palatable and available forage for cattle," said Cole.
Prussic Acid:
Prussic acid, sometimes referred to as cyanide poisoning, typically occurs shortly after cattle are turned on a field that contains the high risk plants such as johnsongrass or sorghum sudan. It is more risky when the forage is less than 18 to 20 inches tall.
"The potential is increased when high levels of nitrate fertilizer have been applied, especially in phosphorus-deficient soils," said Cole.
There is not a simple field test available for prussic acid. The general recommendation is to only turn a few head into the pasture and watch them closely for 30 to 45 minutes. It is also wise to have your cell phone and your vet's number handy in case one or more animals go down.
"The good news is we've not seen many problems directly attributable to prussic acid recently. However, it is always best to error on the side of safety," said Cole.
Cattle seem to adapt to prussic acid if they are on it continuously from springtime through the grazing season. There is a risk in the fall if plants send up new, tender growth following the dry weather or a frost.
"The process of hay making does eliminate the prussic acid risk in most instances," said Cole.
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