A Word of Caution About Some Summer Annual Grasses

Sudangrass and sorghum-sudan contain prussic acid. Compiled by staff

Published on: Jul 20, 2004

Summer annual grasses are a grazing option some drought-stricken producers are depending on for their cattle.

But Bruce Anderson, University of Nebraska forage specialist, warns that sudangrass and sorghum-sudan contain a compound called prussic acid that is potentially poisonous. Prussic acid often is higher during dry weather, so use a few precautions to avoid problems.

Most importantly, do not turn hungry animals into sudangrass or sorghum-sudan pastures.

"They may eat so rapidly that they could get an overdose of prussic acid," Anderson says. "Secondly, since the highest concentration of prussic acid is in new shoots, let the grass get a little growth on it before grazing to help dilute out the prussic acid."

Begin grazing sudangrass at about 18 inches in height, but wait until sorghum-sudan hybrids are 20 to 24 inches tall before grazing because they usually contain a little more prussic acid.

If you planted pearl millet, there is no need for the grazing precautions. Since pearl millet does not contain prussic acid, let animals graze it when it reaches 12 to 15 inches tall.

Summer annual grasses respond best to a simple, rotational grazing system, Anderson says. Divide fields into three or more smaller paddocks of a size that permit your animals to finish grazing each paddock within 7 to 10 days.

"Graze plants down to about 8 or so inches of leafy stubble before moving to the next paddock," he notes. "Repeat this procedure with all paddocks. If some grass gets too tall, either cut it for hay or rotate animals more quickly so grass doesn't head out."