Guidelines for grazing sudangrass, pearl millet and sorghum

A field of sudangrass

By Bruce Anderson
University of Nebraska-Lincoln

Summer annual grasses planted this spring soon could be ready to graze. Let’s review some grazing guidelines to help you avoid any potential hazards or problems. 

It’s been said that rules are meant to be broken. One rule, though, that I suggest you never break is this one: never turn hungry animals into sudangrass or sorghum-sudan pastures. Why? Because they may eat so rapidly that they could get a quick overdose of prussic acid and die. 

All sudangrass and sorghum-sudan hybrids can produce a compound called prussic acid that is potentially poisonous. Prussic acid, which also is called cyanide, is nothing to fear, though, as long as you use a few precautions to avoid problems. 

The highest concentration of prussic acid is in new shoots, so let your grass get a little growth on it before grazing to help dilute out the prussic acid. Let sudangrass get at least 18 inches in height before grazing. Since sorghum-sudan hybrids usually have a little more prussic acid risk, wait until they are 20 to 24 inches tall. 

Pearl millet does not contain prussic acid so if you planted millet these grazing precautions aren’t needed. Let your animals graze pearl millet when it reaches 12 to 15 inches tall. 

Summer annual grasses respond best to a simple, rotational grazing system. Divide fields into three or more smaller paddocks of a size that your animals can graze down to about eight or so inches of leafy stubble within 7 to 10 days. 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. 


A well-planned start, a good rotation, and a little rain can give you good pasture from these grasses all the rest of the summer.

(This article is reprinted from the August 2014 issue of "Forage News", published by the University of Kentucky Extension Service.)