NORTH PLATTE, Neb. — Summer annual crops like forage sorghum, sudangrass, and sorghum/sudan hybrids may have been grazed or harvested once already this year. With adequate moisture, these crops have the potential to grow back and produce another harvest opportunity, but need to be managed correctly to avoid potential hazards.
Sorghum and sudangrass species have the potential to build toxic levels of prussic acid in new shoots. This goes for regrowth as well, so proper management when grazing is essential. New growth needs to be 15-18 inches high in sudangrass and 18-24 inches high in sorghum/sudan hybrids before grazing can safely occur. In regrowth, new shoots can come out at different points from the remaining stalk, so make sure to measure the new growth’s actual height, not just from the ground up.
One nice thing about prussic acid is it converts to a gas in the leaf soon after harvest. While this doesn’t do grazing animals any good, sorghum species cut for hay can dissipate a majority of prussic acid before baling. Similarly, between harvest and the ensiling process, most sorghum/sudan hybrids harvested for silage have lowered prussic acid to safe levels by feed out.
With heat and dry conditions creeping back across the state, all stressed summer annual grasses, including our millet species, have the potential to accumulate nitrates, especially when drought stressed. Unlike prussic acid which dissipates when cut for hay, nitrates stick around, so whether grazing or haying, cut high to avoid portions of the plant where concentrations are highest. Harvesting plants that are at high nitrate risk for silage may be the safest option, as the ensiling process naturally reduces nitrate levels. However, a forage nitrate test should be taken before feeding to ensure levels are safe.
Summer annuals are great forage opportunities, especially when multiple harvests are available. With proper management the risk of prussic acid and nitrates can be mitigated, so you can get the most out of these summer forage kings.
— Ben Beckman, Nebraska Extension
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