Avoid Prussic Acid in Sorghum Crops: Harvest Appropriately

Clippings — October 24, 2019

Frost-damaged or killed forage sorghums, sorghum-sudangrasses or sudangrasses can produce good feed and be safe from prussic acid issues if harvested at the right time and harvest method. Continue as usual when harvesting as baleage, silage, or dry hay. Farmers should take grazing livestock off those crops if frost is predicted and should not greenchop frost-damaged sorghums to prevent prussic acid poisoning, says Jeff Jackson, Alfalfa & Forage Specialist with Croplan by WinField United.

Whether sorghums show partial-leaf, whole-leaf or whole-plant frost damage, cell membranes inside damaged leaves rupture and prussic acid gas – equivalent to Cyanide gas – is produced, Jackson warns. Livestock abortions or death can result. When toxins are allowed to dissipate first, the crops are safe to feed, he adds.

“Generally, if you’re going to do silage, baleage or dry hay, continue on with the process. If you’re going to do silage, you might also swath it, wilt it for a couple of days, and chop it into small (1”) pieces. As you chop the small leaf material, it’s going to let the (prussic acid) gas escape faster. By the time you have a few lag days to wilt, get it to the right moisture, ferment, and leave it stored for a while, you should be fine to feed this crop.” Chopping standing crop will keep it off the ground to avoid additional ash content in feed; it also allows for a higher chop height to leave the least digestible and/or highest nitrate portion in the field.

Harvesting baleage generally involves swathing to crimp and lay the crop in a wide windrow to drop moisture to an acceptable ensiling level. Crimping mechanically manipulates leaves to help gases quickly disperse. The number of tons harvested will increase, as the crop can be cut lower; however, overall quality will decrease and, potentially, whole-plant nitrate levels can increase if in an area of concern.

By the time sorghum crops can be stored as dry hay, the gases will be released or will release during storage. There are a few options to utilize lodged crop as feedstuffs, too. Those include using a gathering head on the chopper or a swather or discbine head to windrow crop for baling or chopping. Farmers can also use a flail-chopper type of stalk chopper or windrower, and maybe rake to get good windrows, or they can graze lodged crop after the poison dissipates.

“Our two big concerns are grazing and greenchop” right after a frost hits, Jackson says. By taking cattle off grazing when frost threatens, farmers remove the chance of prussic acid poisoning. If frost-damaged or killed sorghums are greenchopped, the prussic acid gas is hauled along to bunks and not given time to escape from the leaf material, the specialist adds.

He advises growers to examine sorghum crops right after a frost or low temperatures occur to check for leaf or plant damage. At times, plants won’t show damage until the next day or so. Those plants aren’t safe to graze and/or greenchop until 10-14 days after a frost – if another frost doesn’t occur in the meantime.

Jackson also suggests checking for new tiller growth on damaged plants. “Let’s just say a whole plant froze; it looks dead all the way from top to bottom. In about 10 days you want to look at the bottom of that plant. If it … doesn’t freeze hard enough to kill the plant completely, you might have some tillers that try to regrow from the bottom. Those will be toxic as well, and the plant has to refreeze again to kill it hard enough to get rid of those tillers. Then you have the (10- to 14-day) waiting period again.”

Farmers have asked Jackson how much prussic acid can kill a cow. His answer: “If I told you I had a glass of lemonade, but there is a little bit of Cyanide poison in there, how much of that do you want to drink? So there’s the message. Do you want to take a chance of an abortion or a dead cow due to prussic acid?”

Jackson offers timely crop videos on as ForageFanAddict (one word) and on Twitter as Forage FanAddict (two words).
Clippings – October 24, 2019

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