With a forage shortage imminent, more than the usual number of acres were seeded this year to forage sorghum or sorghum x sudangrass hybrids.  The question always arises this time of year regarding how to handle sorghum related species following a fall frost to avoid prussic acid poisoning in livestock.  Prussic acid is converted in the plant from another compound called dhurrin.  The conversion rate is highest when plant tissue is injured, as in a frost event.  Below are some management recommendations as they relate to sorghum species and the potential for prussic acid poisoning: 

·       Sorghum-sudan hybrids should be assumed safe to harvest or graze after they reach 18-24 inches in height.  The highest levels of prussic acid are generally found in young/short shoots of sorghum-sudangrasses.

·       Prussic acid levels are reduced 50 to 70 percent during field curing.  Conditioning stems is beneficial for reducing prussic acid levels.  Thus, a field wilted crop for silage or dry hay will have far less prussic acid poisoning potential than a grazed or green chopped crop.

·       The fermentation process may further reduce prussic acid levels.

·       All sorghums having adequate growth for safe grazing before frost can be grazed safely 5 days after frost if the frosted plants have dried out. This means sudangrass or sorghum-sudan hybrids over 18-24” tall.   Frosted sorghum is very dangerous until it has dried out, so wait until the plant material is dry.

·       Wait 2 weeks after a killing frost before grazing sorghums that are too short for safe grazing before frost.

·       If new shoots develop after a partial frost killing, don’t graze any sorghums until complete frost killing occurs. The new shoots are especially high in prussic acid potential and may be preferred by livestock.

·       If possible, harvest sorghum-sudangrass BEFORE a killing frost rather than waiting until after the fact.