Feed produced during a drought may have higher levels of nitrate than would be safe for livestock consumption. Ruminant animals, such as cattle and sheep, are susceptible to nitrate poisoning because of their digestive process. Nitrate is converted to nitrite in the rumen. When nitrite moves into the blood stream it prevents the blood cells from carrying oxygen, resulting in suffocation. Abortions can also occur in cows where lower levels of nitrates are fed.
Drought-stressed forages from oats, barley, and corn account for most of the nitrate poisoning cases in North Dakota. However, a number of other crops can also accumulate nitrate, including wheat, sudan grass, sorghum sudan hybrids, turnips, and pearl millet along with certain weeds, especially kochia.
Extension agents in this area have reported that many annual forage samples are coming back above acceptable levels for nitrates so testing for nitrates should be strongly considered before fields are grazed or before harvested feeds are fed. Testing is cheaper than losing livestock.
Nitrate levels can sometimes be reduced by ensiling annual forages, but, unfortunately, they generally remain constant in forages cut and cured for hay and don’t dissipate over time.
Hay with higher than acceptable levels of nitrates can often still be utilized as feed but must be blended with other low-nitrate feeds. Blending is best accomplished by feeding a total mixed ration using a feed wagon. Hay grinding can also be an option by grinding high and low nitrate hays together in the proper proportions. However, don’t just set bales out or roll out bales expecting cattle to blend the hays on their own.
In addition to nitrates, drought stressed conditions can also increase the risk of prussic acid poisoning with sorghum or sorghum sudan hybrids. Prussic acid is similar-to nitrates in that it binds to the hemoglobin in the bloodstream which hinders oxygen transfer and can result in asphyxiation. Symptoms of prussic acid poisoning appear rapidly, within minutes of the livestock consuming forage. Immediate symptoms include staggering, labored breathing, spasms, and foaming at the mouth. Affected animals will often lie down and begin thrashing and if treatment isn’t administered quickly it will result in death.
Prussic acid poisoning is more of a concern if you plan to graze sorghum or sorghum sudan crosses and testing should be strongly considered before turning livestock out on sorghum sudan stands or mixtures containing sorghum sudan.
If samples come back marginal or unsafe, you can probably still utilize the forage but in a different fashion. Unlike nitrates that generally remain constant when cut for hay, prussic acid is volatile, and levels will drop as the plants die and dry down. As such, swathing the sorghum sudan and putting it up for hay would be one option. A couple other options would be to swath and then swath graze following a 7 to 10 day waiting period to allow the prussic acid to volatilize or wait to graze until 7 to 10 days after a hard, killing frost.
The best source of information on sampling, testing, and interpreting results on nitrates or prussic acid is the NDSU Extension Service. Contact your local extension agent for more information.