Prussic acid is present in appreciable amounts only in the rapidly growing part of the plant, which is a very small portion of a sudangrass plant 18 to 20 inches or more in height and a sorghum-sudangrass plant 24 to 30 inches or more in height. The same is true of new growth following a frost that kills the tops but not the crowns of the plants, and the new growth brought about by rains following a drought. Feed hay to hungry livestock before turning them into sudangrass or sorghum-sudangrass hybrids for the first time. It might also be helpful to permit grazing for only a short period of time the first day. Livestock turned into a field of sudangrass or sorghum-sudangrass that is high in prussic acid usually will stop eating in 10 to 15 minutes if they are not too hungry.
Livestock vary in the amount of prussic acid that it takes to be fatal.
Frosted sudangrass and sorghum-sudangrass hybrids can be very dangerous if pastured before the plants have thoroughly dried. Immediately after frost, remove the animals from the pasture until the grass has dried out, usually 5 to 6 days. If new shoots develop after a frost, use the forage as hay or silage rather than pasture. Frosted sudangrass and sorghum-sudangrass hybrids can be safely used for hay or wilted silage. Use tester animals if you are going to feed questionable hay, when there is reason to question the safety of grazing or green feeding, or when the silo or bunker is freshly opened.