Sudan Grass

Early Growth of Sudan Grass

Information from the Goverment of Ontario, Canada on Sorgham-Sudan Grass.

This is a fine stemmed and leafy plant with very quick regrowth. It is best used for pasture or in multiple cut systems. If used in a one cut system, yields will be less than that of Sorghum. Forage quality will be high due to low fiber content if cut frequently.

CAUTION: Members of the Sorghum family contain dhurrin, a glucoside that breaks down to release hydrocyanic acid also known as prussic acid. A sudden disruption of growth such as frost, drought or cutting, causes prussic acid to be released inside the plant at a more rapid rate. High prussic acid levels may be lethal to cattle. Prussic acid will breakdown in one to two weeks, so material made into hay or silage is safe to use.

Prussic acid poisoning is a concern in feeding Sorghum, Sudan grass, or Sorghum-Sudan grass hybrids. These species contain varying amounts of cyanogenic glucosides. In the rumen, these compounds are converted into prussic acid, which is readily absorbed into the blood. High blood levels of prussic acid interfere with respiration and cattle can soon die from respiratory paralysis. Horses should not be allowed to graze these plants as they may develop cystitis syndrome. This condition looks like colic with accompanying bloody urine and can be fatal to horses. Affected animals may show a staggering gait and urine dribbling. Pregnant mares may abort. There is no treatment for this poisoning and poor prognosis of recovery. Some species and varieties contain low levels of cyanogenic glucosides (e.g. Piper sudan grass). The management practices below can reduce risk of prussic acid poisoning:

- Graze or green chop only when forage is greater than 45 cm tall (18 inches ) for Sudan grass or greater than 55 to 65 cm (22-26 inches) for Sorghum, Sorghum-Sudan grass hybrids.
- Don't graze plants......................
  • during or immediately after a drought, or under conditions where growth has been reduced
  • on nights when a frost is likely. High levels of the toxic compounds are produced within hours after a frost occurs
  • after a killing frost
  • until the plant is dry and brown ascyanogenic glucosides usually dissipate within 7 days.
  • after a non-killing frost until regrowth is at least 45 cm (18 inches) tall
- Don't green chop or ensile the forage for 3 to 5 days after a killing frost.
- Allow forage to ensile for at least 3 weeks before feeding.

Nitrate poisoning and formation of toxic silo gas can be a problem with Sorghum-Sudan grass. High nitrate levels are only a problem under abnormal growing conditions such as:
  • High nitrogen fertilization caused by heavy fertilizer or manure applications or following legume plow down.
  • Prolonged drought followed by rain.
  • Any condition which kills the leaves while the roots and stems remain active will initiate accumulation of nitrates (frost, hail, grazing and trampling, or sometimes drought and overcast weather).
Under these conditions, plants accumulate high levels of nitrates. When animals eat these plants, the nitrates are converted rapidly to nitrites which are absorbed into the blood. Nitrite in the blood alters the way the blood carries oxygen. This causes rapid breathing, fast and weak heartbeat, muscle tremors, staggering and death if corrective steps are not taken. The same precautions for prussic acid poisoning will help prevent nitrate poisoning.

In spite of these potential problems with Sorghum-Sudan grass, it is a good emergency forage during summer conditions.

See more information at Sudan-grass.
From Kellogg's Seed Service:
Poisoning - more livestock has been poisoned on nitrates than from prussic acid in California. Nitrate poisoning is usually the result of over fertilizing with nitrogen or by moisture stress with high nitrogen leaves. Prussic acid comes on after a hard freeze in late fall, early winter. Sorghum-Sudan hybrids are not recommended for horses for grazing - some feel they can cause 'circling disease in horses'. For all these cautions we have very few problems and they are usually years apart. See more details here.
There are various articles that report that sudan grass is poisonous to cattle, sheep, and horses. For additional information and before feeding to llamas and alpacas, check with your local veterinarian and your county extension agent. Also check out various lists of poisonous plants or do a search for sudan grass, Sorghum-Sudan grass, or sorghum.

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