Prussic acid is released very rapidly from the glucoside form in frozen leaves. This is the reason that frosted sorghum is dangerous to feed until it dries out. There is little danger of prussic acid poisoning in grazing most varieties of sudangrass. Plants that have a height of about six feet tend to not affect animals as much as shorter, stunted, plants experiencing regrowth. Favorable weather for plant regrowth after clipping, drought, frost, or grazing will result in new leaves that are likely to be very toxic and cause prussic acid poisoning.
Small shoots are high in cyanide content and are desirable to cattle.
Accumulate high levels of cyanide early in growth stage i.e. new growth after frost, after heavy nitrate fertilization Accumulate high levels of cyanide during periods of stress i.e. frost, drought, herbicide kill Cyanide is more concentrated in young leaves than in older leaves or stems. New sorghum growth following drought or frost is dangerously high in cyanide. Pure stands of Indiangrass that are grazed when plants are less than 8 inches tall can posses lethal concentrations of cyanide. Prussic acid poisoning is most commonly associated with regrowth following a drought-ending rain or the first autumn frost. New growth from frosted or drought-stressed plants is palatable but dangerously high in cyanide.