Forage sorghums should be tested before cutting
Jul 20, 2009 10:43 AM, By Donald Stotts, Oklahoma State University
Searing summertime temperatures have been topping the century mark, and that means cattle producers need to take steps to ensure high concentrations of nitrates have not accumulated in forage sorghums prior to use.
“These high-nitrate plants, either standing in the field or fed as hay, can cause abortion in pregnant cattle, or even animal death if consumed in great enough quantities,” said Glenn Selk, Oklahoma State University Cooperative Extension livestock specialist.
Producers need to remember that nitrates do not dissipate from sun-cured hay, unlike prussic acid. Therefore, once the forage is cut for hay the nitrate levels remain constant.
The major sources of nitrate toxicity in Oklahoma and surrounding areas will be summer annual sorghum-type plants such as sudan hybrids, sorgo-sudans, millets and Johnsongrass, among others.
“We recommend producers test summer annual hay fields before they cut,” said Nathan Anderson, Payne County Extension director and agricultural educator. “Experience tells us that we cannot estimate nitrate content just by looking at a field.”
Testing before cutting gives producers an additional option of waiting for normal plant metabolism to bring the nitrate concentration back to a safe level before harvesting.
“Another useful tool is to raise the cutter bar when harvesting the hay,” Anderson said. “Nitrates are in greatest concentration in the lower stem. Raising the cutter bar may reduce the tonnage, but cutting more tons of a toxic material provides no particular value.”
Anderson said producers should remember that raising the cutter bar will not totally eliminate nitrate toxicity in the plants.
“If a producer has any doubt about the quality of the hay, send a forage sample to a reputable laboratory for analysis to get an estimate of nitrate concentration,” he said. “This will provide guidelines as to the extent of dilution that may be necessary to feed the hay to cattle more safely.”
Selk added that it is always a good idea to let cattle become adapted to nitrate in hay. By feeding small amounts of the forage sorghum along with other feeds such as grass hay or grains, cattle begin to develop a capability to digest the nitrate with less danger.
“It’s summer now but it will be winter when the hay is fed; producers should remember to avoid the temptation of feeding high-nitrate forage for the first time after a snow or ice storm,” he said.
In such conditions, cattle will be stressed, hungry and not adapted to the nitrates. They are likely to consume unusually large amounts of the forage, increasing the potential for nitrate toxicity.
Selk and Anderson recommend that producers read OSU Extension Fact Sheet No. 2903, “Nitrate Toxicity in Livestock,” before cutting or feeding any sorghum forage hay. The fact sheet is available at http://osufacts.okstate.edu/docushare/dsweb/Get/Document-1996/PSS-2903web.pdf on the Internet.
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