High nitrate and prussic acid concentrations can be deadly for cattle, said Dirk Philipp, assistant professor for the University of Arkansas System Division of Agriculture.
Prussic acid is common in sorghum species such as forage sorghums, sorghum-sudan varieties, and Johnsongrass. Poisoning happens when cattle eat leafy growth stressed from severe conditions such as drought.
Farmers and growers should pay extra attention because these grasses attract livestock.
Don’t put hungry cattle out in a field of sorghum or Johnsongrass, he said. “Feed them hay or any other safe forage before entering the field.”
Besides drought, over-fertilization can be a big contributor to prussic acid. Even though nitrogen fertilizer can help produce high yields of sorghum forage, the lack of soil phosphorus and potassium may lead to high concentrations of prussic acid.
Cattle producers should “graze plants only after they reached 18-24 inches,” he said. “Prussic acid is mainly contained in leaves, thus low-growing leafy plants may contain dangerous levels of Prussic acid.”
Wilted plants or drought-damaged sorghums should not be grazed until at least five days have elapsed since a good amount of rain.
When cooler weather returns, growers should also be aware that frost damage can also render forages dangerous.
Philipp said that even if a sorghum forage pasture cannot be grazed, “hay can still be made as prussic acid concentrations will drop during the curing process and usually will not be toxic to animals.”
Source:uaex.edu