Common Name
Sudan grass
Botanic Name
Sorghum sudanensis
Plant Family
Poaceae (Gramineae)
Often grown as a forage or cover crop in dry areas.
Animals Affected
Cattle, sheep, horses
Toxic Principle
Cyanogenic glycosides which are hydrolysed by rumen microorganisms to free hydrogen cyanide (HCN). All parts of the plant are poisonous especially if wilted or in regrowth. The Cyanide blocks the action of the cellular enzyme cytochrome oxidase thus preventing hemoglobin from releasing oxygen to the tissues. Death results rapidly from anoxia. Sudan grass may also accumulate toxic levels of nitrates.
Drought tolerant plant growing 5-8 feet tall, with scaly root stalks and relatively broad leaves with a prominent mid vein. Seeds are yellow-purple and occur in a large, many branched panicle. Sudan grass and its hybrids are very similar in appearance, and tend to be more robust plants than Johnson grass, having broader leaves and thicker stems. The seed heads are produced terminally and in some hybrids contain much larger seeds than Johnson grass.
Posterior ataxia is common in chronic Sudan grass poisoning.
Without stressing the animal, sodium thiosulfate and sodium nitrite should be given intravenously. A mixture of 1ml 20% sodium nitrite and 3ml of 20% thiosulfate should be prepared and given at the rate of 4 ml of the mixture per 100lbs body weight. Sodium thiosulfate should be given orally via stomach using 30gm dissolved in a gallon of water.
Cardiovascular system
Mucous membranes appear cherry-red. Venous blood is cherry-red in color. Stressing the animal rapidly leads to collapse and death. If the sSudan grass is high in nitrates, the blood will be brown in color due to the formation of methemoglobin.
Respiratory System
Initially animals show difficulty in breathing. Open mouth breathing is common as the animal becomes oxygen deprived.
Nervous System
Horses andcattle consuming Sudan grass for prolonged periods, develop a syndrome of posterior ataxia, urinary incontinence, cystitis, and weight loss. The disease results from lower spinal cord degeneration induced by low levels of cyanogenic glycosides (Lathyrogens)in the plants that cause demyelinization of the peripheral nerves.
Renal System
Urinary incontinence, cystitis are typical of chronic Sudan grass poisoning.
Reproductive System
Abortions may occur if the dam does not die from the acute effects of the cyanide.
Rumen contents or plant material can be tested for eyanide using the sodium picrate test. Commerical test kits for cyanide are available. If high in nitrates, methemaglobin levels in affected animals will be elevated.
Special Notes
Certain varieties of Sudan grass hybrids have been developed that do not contain cyanide and therefore should be selected for feeding livestock so as to avoid the chronic cyanide toxicity problem. NITRATES: See Kochia weed for comments on managing nitrates in forages for cattle.