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Beware of cyanide (prussic acide) poisoning

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By Rick Greenwell

We received this information from Michelle Arnold, Cindy Gaskill and Ray Smith, University of Kentucky Specialist  in the Forage newsletter. We thought it was a very good information and wanted to share it with you.

With the start of fall comes the risk of cyanide poisoning in ruminants. Cyanide, prussic acid, hydrogen cyanide or hydrocyanic acid poisoning are all terms describing the same condition. A number of common plants, including sudangrass, johnsongrass, sorghums and sorghum-sudangrass hybrids contain cyanogenic glycosides in the outer cells of the plant. Further inside the leaf tissue are the enzymes needed to convert these compounds to the cyanide poison. When the plant undergoes a stressful event such as cutting, wilting, freezing, drought, crushing, trampling, chewing or chopping, the plant cells rupture which allows the cyanogenic compounds and the enzymes to combine and produce hydrogen cyanide gas. Ruminants also have enzymes in the rumen capable of converting the cyanogenic compounds in the plant into cyanide. The toxic gas goes to the bloodstream and blocks a necessary step in the release of oxygen from red blood cells. The animal essentially dies from lack of oxygen. Clinical signs of cyanide poisoning can occur within minutes to hours after consuming the toxic forage. Usually the affected animals are found dead, but if observed early, may show rapid, difficult breathing, frothing at the mouth, muscle tremors, staggering and then collapse. The mucous membranes (such as the gums) are bright pink and the blood can be a bright cherry-red color.

It is important to recognize and avoid situations in which these forages pose a danger to livestock. Cattle and other ruminants should only graze sorghum, sorghum hybrids, or johnsongrass when the plants have reached at least 18-24 inches in height. Do not graze plants with young tillers. Do not graze these plants during drought periods when growth is severely reduced or the plant is wilted or twisted and wait at least one week after rainfall to resume grazing. Do not graze at night when frost is likely. Frost allows conversion to hydrogen cyanide within the plant. Do not graze for two weeks after a non-killing (>28 degrees) frost. It is best not to allow ruminants to graze after a light frost as this is an extremely dangerous time and it may be several weeks before the cyanide potential subsides. Do not graze after a killing frost until plant material is completely dry and brown.

If a high cyanide is suspected in forages, do not graze or feed as green chop. If cut for hay, allow at least 72 hours or longer before baling so that the cyanide will dissipate. Allow thorough drying because toxicity can be retained in cool or moist weather. Delay feeding silage six to eight weeks following ensiling.

If you have questions concerning testing for cyanide in forages, call your county agricultural extension agent for further information.

Nitrate rumors can kill cattle
The following information is from Bruce Anderson, University of Nebraska.
Neighbors, friends and coffee shops can give great advice, but lately some of the information being spread about nitrates in corn stalks is wrong and could prove deadly. More in a moment.

Watch for rumors about nitrates in corn stalks. Some rumors I’ve heard lately might mislead you into losing some of your cattle.

For example, some people say that after a freeze the nitrates will leave the stalk. So it should be safe to bale or graze corn stalks after it freezes even if the stalks currently contain high nitrates. In real life, though, a freeze probably will have no effect at all on nitrate levels.

Almost all our corn plants will be mature and dead before it freezes this fall. And if some plants are still green and alive, a freeze might actually cause a brief increase in nitrate levels.
Other folks assume it will be safe to graze stalks after grain harvest. And in most situations they are correct, but not all the time. Nitrates do tend to decline as plants mature, and plants that produce grain tend to have lower nitrate concentrations. Also, the husks and leaves that cattle prefer only rarely have high-nitrate concentrations.

But notice that I didn’t say always. I used the words tend and rarely. This has been a stressful year. Dryland fields still may have high nitrates, especially in that lower stalk. You may be tempted to force animals to graze stalks a bit harder than usual this year. Cattle may start out selecting safe husks and leaves, but as that supply declines they will graze more of the lower stalks with potentially-dangerous nitrate concentrations.

Play it safe. Before grazing, sample your stalks. Check nitrates in the lower foot of stalk. Check nitrates in the upper portion along with leaves and husks. What you discover could save your animals’ lives.