Beware of frosted sorghum grasses

Wednesday, November 1, 2017

The autumn frosts are rapidly approaching, and while the cool weather is usually good for grasses like tall fescue and orchardgrass, livestock producers should be aware of using grasses in the sorghum family during this period.

Grasses in the sorghum family, such as sorghum, sorghum-sudan, and johnsongrass, can be toxic after a frost. The frost causes the release of prussic acid, or hydrocyanic acid. Tender, young growth is more likely to be toxic than older, mature growth. Grazing sorghums that have been frosted have the potential to be deadly. Pearl millet and crabgrass does not release prussic acid.

Symptoms associated with prussic acid poisoning include excessive salivation, rapid and labored breathing, and muscle spasms. These symptoms may occur within 10-15 minutes of the animal eating the poisoned forage. Animals may stagger, collapse and eventually die. Death is caused by the prussic acid interfering with the oxygen-transferring ability of the red blood cells and essentially causing suffocation.

To minimize the potential for prussic acid poisoning, follow these recommended management practices:

1. Do not graze for one to two weeks after a frost.

2. Utilize sorghums as hay after frost.

3. Do not feed silage cut from a frosted field for 6 weeks following ensiling.

Prussic acid usually dissipates in 7-10 days following a frost, but extra care should be taken to avoid potential poisoning. Making hay out of the forage will minimize the potential for poisoning. For more information, contact the UT Extension Marshall County office at (931) 359-1929 or visit UT Beef and Forage Center website at