Grazing Sorghum Following Frost and Prussic Acid - October 10, 2023 - Amy Timmerman - Extension Educator
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- [0:00] This is Amy Timmerman with Nebraska Extension.
- [0:04] Cover crops, soil health, extended grazing, and
- [0:07] 13-way mixes are all buzzwords in the agronomic world today.
- [0:12] Whether you are using cover crops for additional grazing or planting
- [0:15] them with the intent to improve your soil, it’s important to make sure
- [0:19] the mix will truly fit your needs and not cause issues later.
- [0:22] When cover crops become a forage crop it’s important to treat them as such and
- [0:26] to understand the risks associated with utilizing them as supplemental forage,
- [0:31] especially as our environmental conditions begin to change.
- [0:35] This becomes critical as we move into the fall months.
- [0:38] As summer turns into fall, freezing temperatures
- [0:41] are making their way across the plains and Midwest.
- [0:45] These freezing temperatures will play a key role in determining
- [0:48] what can be grazed or hayed safely for your livestock.
- [0:51] Taking a quick peak at your seed tag before grazing or haying is key.
- [0:55] Maybe you have decided to try a new 13-way mix
- [0:58] and don’t have all the components memorized?
- [1:01] Perhaps this is your first time using cover crops?
- [1:04] These mixes may be unfamiliar or new to your system and
- [1:07] could be hazardous if fed incorrectly.
- [1:10] When cover crops become forage, they need to be treated as such.
- [1:14] Freezing temperatures cause metabolic and
- [1:17] cellular changes to our forage crops,
- [1:20] specifically prussic acid formation is one of the biggest concerns.
- [1:24] Sorghum, sudangrass, sorghum-sudangrass hybrids,
- [1:29] and milo following a frost have broken cell membranes
- [1:32] that allow the formation of prussic acid.
- [1:35] Prussic acid is a form of cyanide released from a compound called durrin
- [1:39] that is naturally occurring in sorghum species.
- [1:43] When ingested and broken down by the digestive system,
- [1:46] the cyanide is released can quickly cause lethal results
- [1:50] when consumed in high amounts.
- [1:52] Monogastric species like pigs and horses can get
- [1:55] prussic acid poisoning in extreme cases,
- [1:58] but ruminants are more susceptible.
- [2:00] Keeping livestock out of these areas for five to seven days after a frost
- [2:06] can limit the risk associated with prussic acid.
- [2:09] Each time a new part of the plant is frozen,
- [2:12] this five-seven day timer is reset until the entire plant has been killed.
- [2:17] This can make grazing difficult this fall when freezing events occur
- [2:22] regularly but are not enough to fully kill the plant.
- [2:25] New shoots and especially regrowth on previously frost-damaged plants have the
- [2:30] highest concentrations of prussic acid.
- [2:32] If you notice new shoots after a frost, animals should not be allowed to graze
- [2:37] until the regrowth is 15-18 inches tall or a frost completely kills the plant.
- [2:42] This can be especially tricky when warm temperatures follow an early frost.
- [2:47] Unless extremely high levels of prussic acid are present initially,
- [2:51] haying or cutting a crop with prussic acid is not a concern.
- [2:55] During the drying process, the prussic acid will volatilize and
- [2:59] 50% or more of the initial concentration will be lost.
- [3:03] Similarly, the fermentation process for ensiled
- [3:07] sorghums will reduce prussic acid levels.
- [3:09] If you are concerned about high levels of prussic acid in a
- [3:13] silage or hay feed, samples can be sent to a lab for analysis.
- [3:17] If you have further questions regarding prussic acid,
- [3:21] please reach out to your local extension office.
- [3:24] This has been Amy Timmerman with Nebraska Extension.