Grazing Summer Annual Grasses

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Many livestock producers use summer annuals to supplement or enhance summer grazing. Sudex or sorghum-sudan hybrids, sudangrass and Pearl millet are the most used varieties.

Much of the sudangrass and sorghum-sudan grasses planted this spring will be ready to graze soon, so producers should keep in mind they contain a compound called prussic acid that can be toxic. Prussic acid often is higher during dry weather so use a few precautions to avoid problems.

The highest concentration of prussic acid is in young shoots, so let the grass get a head start 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, as they typically contain higher prussic acid levels. If using pearl millet, there is no need for these precautions because it does not contain prussic acid. Pearl millet can be grazed when it reaches 12 to 15 inches tall.

Summer annual grasses work best with a simple, rotational grazing system. Divide fields into smaller paddocks that will allow grazing for 7-10 days. Graze grass down to about 8 inches of stubble then move to the next paddock. Repeat this procedure with all paddocks. If grass gets too tall, either harvest it for hay or rotate animals more quickly to prevent it from heading.

It’s best not to turn hungry animals into sudangrass or sorghum-sudan pastures. They may eat so rapidly that they could get an overdose of prussic acid.

With a well-planned start, pasture rotation and some needed rain, you can have abundant forage for the rest of the summer.
summer annual grass pasture