Beef producers have long realized substantial benefits by using warm-season annuals to produce forage during the midsummer when tall fescue and other cool-season grasses are poor in nutritional quality and have only limited growth. One of the most popular warm-season annuals used is sorghum-sudan grass. This plant has the positive benefits of ample forage production and high nutritional quality. One of the negative aspects of sorghum-sudan is its ability to produce cyanide. When plant growth and environmental conditions are correct, the plant will contain high enough levels of cyanide to be toxic to cattle that consume the sorghum-sudan. One of the environmental conditions that can cause elevated levels of cyanide is drought.
The cyanide contained in sorghum-sudan is in a chemical form referred to as prussic acid. New growth material on the plant will typically contain high levels of prussic acid. When cattle consume the new growth, the prussic acid is digested and the cyanide is released and absorbed by the animal. The amount of cyanide absorbed can be sufficient to kill the animal. This is the reason that grazing sorghum-sudan is done after the plant has had some time to grow.
In drought conditions, the plant will respond to rainfall by rapid growth of new leaf shoots. The leaf shoots will contain high levels of prussic acid. When cattle are being grazed on sorghum-sudan during the midsummer and drought occurs, the animals need to be managed to prevent consumption of new growth material that occurs once the drought breaks. As precautionary steps, don’t graze the sorghum-sudan until the plant is over 18 inches in height, or allow approximately one week before grazing after a drought. These general guidelines should provide sufficient time for the prussic acid concentration in the plant to be reduced to nontoxic levels.
Updated 6/15/06
