Each fall, prussic acid poisoning is a serious concern for livestock producers, particularly those growing warm-season sorghum-based forages such as forage sorghum, sorghum-sudangrass, sudangrass, and johnsongrass.
Taking the proper precautions can help protect your livestock and prevent prussic acid poisoning.
Prussic acid poisoning can occur when livestock graze sorghum-based forages after a stressful event, such as frost. These plants can contain cyanide-producing compounds in their outer cells and enzymes deeper within the plant that convert those compounds into poison.
When frost damages the plant, its cells rupture, allowing the compounds and enzymes to mix and produce cyanide. If livestock consume the affected forage, the cyanide interferes with their ability to use oxygen, which can lead to rapid death. Ruminants are especially susceptible because enzymes in their rumen can also convert these compounds into cyanide.
Do not allow your animals to graze fields containing sorghum-based forages for five to seven days after a frost, even if it’s patchy. If a killing frost occurs, do not allow the animals to graze the pasture for at least seven days following the frost.
With time, the forage can dry down, and prussic acid is reduced via volatilization.
Sorghum-based forages can be cut for hay after a frost, but they should be allowed to cure properly before baling. During the curing process, prussic acid dissipates, making the hay safer to feed to livestock.
In most cases, you can ensile sorghum forages for baleage because the ensiling process reduces cyanide compounds in the forage. Delay feeding the baleage six to eight weeks after ensiling to allow the fermentation process to finish and toxin levels to decrease. If your forage has particularly high toxin levels at ensiling, you should have the baleage tested before feeding it to livestock.
The best way to prevent prussic acid poisoning is to make the final harvest of susceptible forage species before the first frost, either by grazing or cutting the forage for hay.
If you need to test your forages for cyanide content, contact the Adair County Extension Office at 270-384-2317.
