by Donald Stotts
Parsons, Kansas —
Hot dry summer weather brings about heat and drought stress on summer annuals, wherein stressed plants such as the forage sorghums can occasionally accumulate dangerous concentrations of nitrates for cattle grazing them.
“These high nitrate plants, either standing in the field or fed as hay, can cause abortion in pregnant cattle, and even animal death if consumed in great enough quantities,” said Bob Leadford, Garvin County Extension director and agricultural educator.
Nitrates do not dissipate from sun-cured hay, in contrast to prussic acid; therefore, once the hay is cut the nitrate levels remain constant.
“It’s always a good idea to test hay fields before they are cut, so that the producer knows what he or she has in terms of a safe food resource for livestock,” Leadford said. “Feel free to stop by your local OSU Cooperative Extension county office for testing details.”
Testing the forage before cutting gives the producer an additional option of waiting and allowing for the nitrate to lower in concentration before harvesting the hay. The major sources of nitrate toxicity in Oklahoma will be summer annual sorghum-type plants, including sudan hybrids, sorgo-sudans, sorghum-sudans, millets and Johnsongrass.
Leadford said an excellent resource listing plants that may accumulate nitrates is Oklahoma State University Extension fact sheet PSS-2903, “Nitrate Toxicity in Livestock,” available through the county office or online at http://osufacts.o kstate.edu via the Internet.
“Be aware that drought-stressed corn plants were tested last summer in north central Oklahoma and were reported to test well above the 10,000 parts per million nitrate concentration that is considered potentially lethal to cattle,” said Glenn Selk, OSU Cooperative Extension emeritus animal scientist.
While the risk of poisoning cannot be totally eliminated, OSU’s Division of Agricultural Sciences and Natural Resources recommends the following management techniques to reduce the risk of nitrate toxicity in livestock:
Test the crop before harvesting it. If the crop tested has an elevated concentration of nitrates, the producer still has the option of waiting for normal plant metabolism to bring the concentration back to a safe level.
“It is not possible to estimate nitrate content just by looking at the field,” Selk said.
Raise the cutter bar when harvesting the hay. 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 has no particular value,” Leadford said.
Know the extent of nitrate accumulation in the hay and the levels that are dangerous to different classes of cattle, such as pregnant cows, open cows or stocker steers.
“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 the nitrate concentration,” Selk said. “This will provide the producer with guidelines as to the extent of dilution that may be necessary to more safely feed the hay.”
Allow cattle to become adapted to nitrate in the hay. By feeding small amounts of the forage sorghum along with other feeds such as grass hay or grains, cattle begin to adapt to the nitrates in the feed and develop a capability to consume the nitrate with less danger.
“Time and again there is some producer who cut hay when nitrate levels were high and then used the hay as part of a winter feeding program and had problems at that time,” Leadford said. “Avoid the temptation of feeding the high-nitrate forage for the first time after a snow or ice storm. The cattle will not have adapted to the nitrates; they will be stressed and hungry and often will consume unusually large amounts of the forage.”
Leadford and Selk recommend producers make reviewing OSU Extension fact sheet PSS-2903 part of their normal management plan before cutting and feeding any summer annual hay.£