Sudangrass should not be grazed or green chopped until it has reached a height of at least 18 to 20 inches. Sorghum-sudangrass hybrids should not be grazed or green chopped until they have reached a height of at least 24 to 30 inches. Sorghum is generally unsafe for pasture or green chopping until after plants reach maturity. Species and variety - Sorghums are generally much high in prussic acid than sudangrass. As a group, sorghum-sudangrass hybrids also contain more prussic acid than sudangrasses.
Some varieties tend to be lower in prussic acid than others.
Growers should select varieties with lower prussic acid potential. The free prussic acid in this forage does not begin to decline until thawing and wilting begin. The forage usually is considered safe to feed after drying for 5 to 6 days. A light frost may kill only the tops of the plants and leave the lower portion alive. If favorable weather for growth follows such a frost, these plants will send forth new shoots and leaves which are apt to be very high in prussic acid, and, if pastured, cause cyanide poisoning.