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C.O.R.N
Newsletter
2009-34
October 6, 2009 -
October 13, 2009
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Feeding Frosted Forages
by
Maurice Eastridge, Mark Sulc
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Sorghum and Sudangrass Forages
Prussic acid poisoning can occur when feeding sudangrass, sorghum-sudangrass hybrids, forage sorghum, or grain sorghum. These species contain varying concentrations of cyanogenic glucosides, which are converted to prussic acid, also known as hydrogen cyanide (HCN). As ruminants consume forage containing high levels of cyanide-producing compounds, prussic acid is released in the rumen, absorbed into the bloodstream where it binds hemoglobin, and interferes with oxygen transfer. The animal soon dies of asphyxiation. Prussic acid acts rapidly, frequently killing animals in minutes. Symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse. Ruminants are more susceptible than horses or swine because cud chewing and rumen bacteria help release the cyanide.
Generally, any stress condition that retards plant growth may increase prussic acid levels in plants. Hydrogen cyanide is released when leaves are damaged by frost, drought, bruising, cutting, trampling, crushing, or wilting. Plants growing under high nitrogen levels or in soils deficient in soil phosphorus or potassium tend to have high levels of cyanogenic glucosides. Species and varieties differ in prussic acid poisoning potential. Sudangrass varieties are low to intermediate in cyanide potential, and sorghum-sudangrass hybrids and forage sorghums are intermediate to high. Piper sudangrass has low prussic acid poisoning potential, and pearl millet is virtually free of cyanogenic glucosides. The management practices described below can reduce the risk of prussic acid poisoning from forage sorghum, sudangrass, and sorghum-sudangrass hybrids:
1) Graze or greenchop only when the grass is greater than 18 inches tall.
2) Do not graze wilted plants or plants with young tillers.
3) Do not graze plants during or shortly after a drought when growth has been reduced.
4) Do not graze on nights when frost is likely. High levels of the toxic compounds are produced within hours after a frost occurs.
5) Do not graze after a killing frost until the plants are dry. Wait 5 to 7 days to allow the released cyanide to dissipate.
6) Do not graze for two weeks after a non-killing frost.
7) Delay feeding of silage for 6 to 8 weeks after ensiling. Fresh forage is generally higher in cyanide than silage or hay because cyanide is volatile and dissipates as the forage dries. However, hay or silage that likely contained high cyanide levels at harvest should be analyzed for HCN content before feeding.
8) Split applications of nitrogen decrease the risk of prussic acid toxicity, and proper levels of phosphorus and potassium in the soil will also help.
9) Don't allow hungry or stressed animals to graze young sorghum grass growth.
Nitrate poisoning can occur under conditions of high nitrogen fertilization, heavy manure applications, drought, overcast weather, prolonged low temperatures, or other stress conditions that retard plant growth. Under these stressful conditions, high nitrate levels accumulate in the crop. Once forage is fed, nitrate is converted to nitrite in the animal. When nitrite levels are high, the animal cannot metabolize it quickly enough, and nitrite inhibits oxygen transport in the blood. Symptoms include rapid breathing, fast and weak heartbeat, muscle tremors, staggering, and ultimately death if corrective steps are not taken.
The same management precautions for prussic acid poisoning will help prevent nitrate poisoning. Although pearl millet does not create a potential problem with prussic acid poisoning, it can accumulate high nitrate levels leading to nitrate poisoning. Also, corn for silage should be monitored for nitrate concentrations under conditions described above. High nitrate levels will persist when forages are cut for hay, but ensiling the crop will reduce nitrates by approximately 50%. If forage is suspected of high nitrate levels, have it tested before feeding. |
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C.O.R.N. is a summary of crop observations, related
information, and appropriate recommendations for Ohio
Crop Producers and Industry. C.O.R.N. is produced by
the Ohio State University Extension Agronomy Team, State
Specialists at The Ohio State University and Ohio Agricultural
Research and Development Center. C.O.R.N. Questions
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and the Ohio Agricultural Research and Development Center
at The Ohio State University.
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Ohio State University Extension are available to clientele
on a nondiscriminatory basis without regard to race,
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Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in
cooperation with the U.S. Department of Agriculture,
Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800)
589-8292 (Ohio only) or (614) 292-1868
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