Grazing Sorghum Following Frost and Prussic Acid

Amy Timmerman, Extension Educator Author

10/10/2023 Added

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As summer turns into fall, freezing temperatures are making their way across the plains and Midwest. These freezing temperatures will play a key role in determining what can be grazed or hayed safely for your livestock.

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[00:00:00.859]This is Amy Timmerman with Nebraska Extension.
[00:00:04.170]Cover crops, soil health, extended grazing, and
[00:00:07.841]13-way mixes are all buzzwords in the agronomic world today.
[00:00:12.045]Whether you are using cover crops for additional grazing or planting
[00:00:15.975]them with the intent to improve your soil, it’s important to make sure
[00:00:19.365]the mix will truly fit your needs and not cause issues later.
[00:00:22.666]When cover crops become a forage crop it’s important to treat them as such and
[00:00:26.666]to understand the risks associated with utilizing them as supplemental forage,
[00:00:31.470]especially as our environmental conditions begin to change.
[00:00:35.074]This becomes critical as we move into the fall months.
[00:00:38.734]As summer turns into fall, freezing temperatures
[00:00:41.644]are making their way across the plains and Midwest.
[00:00:45.034]These freezing temperatures will play a key role in determining
[00:00:48.064]what can be grazed or hayed safely for your livestock.
[00:00:51.402]Taking a quick peak at your seed tag before grazing or haying is key.
[00:00:55.832]Maybe you have decided to try a new 13-way mix
[00:00:58.653]and don’t have all the components memorized?
[00:01:01.355]Perhaps this is your first time using cover crops?
[00:01:04.079]These mixes may be unfamiliar or new to your system and
[00:01:07.369]could be hazardous if fed incorrectly.
[00:01:10.289]When cover crops become forage, they need to be treated as such.
[00:01:14.289]Freezing temperatures cause metabolic and
[00:01:17.719]cellular changes to our forage crops,
[00:01:20.019]specifically prussic acid formation is one of the biggest concerns.
[00:01:24.390]Sorghum, sudangrass, sorghum-sudangrass hybrids,
[00:01:29.095]and milo following a frost have broken cell membranes
[00:01:32.873]that allow the formation of prussic acid.
[00:01:35.276]Prussic acid is a form of cyanide released from a compound called durrin
[00:01:39.758]that is naturally occurring in sorghum species.
[00:01:43.408]When ingested and broken down by the digestive system,
[00:01:46.456]the cyanide is released can quickly cause lethal results
[00:01:50.416]when consumed in high amounts.
[00:01:52.802]Monogastric species like pigs and horses can get
[00:01:55.682]prussic acid poisoning in extreme cases,
[00:01:58.292]but ruminants are more susceptible.
[00:02:00.915]Keeping livestock out of these areas for five to seven days after a frost
[00:02:06.505]can limit the risk associated with prussic acid.
[00:02:09.815]Each time a new part of the plant is frozen,
[00:02:12.228]this five-seven day timer is reset until the entire plant has been killed.
[00:02:17.598]This can make grazing difficult this fall when freezing events occur
[00:02:22.118]regularly but are not enough to fully kill the plant.
[00:02:25.109]New shoots and especially regrowth on previously frost-damaged plants have the
[00:02:30.229]highest concentrations of prussic acid.
[00:02:32.939]If you notice new shoots after a frost, animals should not be allowed to graze
[00:02:37.198]until the regrowth is 15-18 inches tall or a frost completely kills the plant.
[00:02:42.391]This can be especially tricky when warm temperatures follow an early frost.
[00:02:47.434]Unless extremely high levels of prussic acid are present initially,
[00:02:51.434]haying or cutting a crop with prussic acid is not a concern.
[00:02:55.733]During the drying process, the prussic acid will volatilize and
[00:02:59.934]50% or more of the initial concentration will be lost.
[00:03:03.804]Similarly, the fermentation process for ensiled
[00:03:07.114]sorghums will reduce prussic acid levels.
[00:03:09.617]If you are concerned about high levels of prussic acid in a
[00:03:13.617]silage or hay feed, samples can be sent to a lab for analysis.
[00:03:17.962]If you have further questions regarding prussic acid,
[00:03:21.246]please reach out to your local extension office.
[00:03:24.456]This has been Amy Timmerman with Nebraska Extension.

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Grazing Sorghum Following Frost and Prussic Acid

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