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Grazing summer annual forages
Forage Minute

Grazing summer annual forages

Cow pastures on Sudan grass

A cow stands in a pasture of Sudan grass at Jamie and Deanne Holmstrom's dairy farm west of New Glarus, Wisconsin. The couple decided to convert to a grain-free operation about 10 years ago, and now pastures 80 mostly-Normande cows on 13 acres of Sudan grass for 12 hours each day throughout the summer.

Summer annual forages such as Sudan grass, sorghum-Sudan hybrids and pearl millet planted this spring soon could be ready to graze. There are some grazing guidelines to help avoid potential hazards.

The first guideline is too never turn hungry animals into Sudan grass or sorghum-type pastures. The reason why is because they may eat so rapidly that they could get a quick overdose of prussic acid and die.

All Sudan grass and sorghum-type 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 young shoots, so let your grass get a little growth on it before grazing to help dilute out the prussic acid. Let Sudan grass get 15 to 18 inches in height before grazing. Sorghum-Sudan hybrids usually have a little more prussic acid risk, so wait until they are 18 to 24 inches tall.

Pearl millet does not contain prussic acid so if you planted millet these grazing precautions aren’t needed. Pearl millet can be grazed when it reaches 12 to 15 inches tall.

Nitrates also can accumulate in these grasses, particularly when there may be droughty conditions and/or excess nitrogen fertilization. However, as long as you avoid grazing too short, nitrates should not be a problem.

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 grass in some paddocks gets too tall, it could be cut for hay.

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.

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