COLUMBIA, Mo. — Drought-stricken forages that accumulate nitrates can kill grazing livestock, quickly, warns a University of Missouri plant scientist.
"We're getting reports of cattle dying," says Rob Kallenbach, MU Extension forage specialist. "As hot weather without rain continues, we expect to hear of more death losses. It happens at the start of every drought."
Large grasses, such as corn, sorghum and sudangrass hybrids, are most often the cause of problems, Kallenbach said on a statewide teleconference Thursday morning. Many plants, even ryegrass and fescue, can accumulate nitrates when soil moisture becomes short.
Johnsongrass and other common weeds can be deadly also.
Nitrogen is essential for forage and grain-crop production. Nitrates are in the plants all the time, creating normal growth. Nitrogen picked up by plant roots from the soil moves up into the plant. Eventually the plant stores that energy in the seed heads as protein.
Nitrates are converted into amino acids, which are building blocks for plant proteins. Protein is an essential part of animal diets.
Lack of moisture stops the flow of nitrates up the plant and the conversion to protein. The roots continue to bring nitrogen into the plant, where it accumulates first in the stalks. Too much unconverted nitrate can become toxic.
In a drought, producers needing forage turn cows to graze corn, sorghum or other large grasses. Usually the only time a farmer grazes corn would be when it is obvious the plant will not make ears of corn for grain harvest. Grazing is considered when drought stops conversion of nitrate into protein.
That's when deadly trouble occurs.
Cornstalks and other plants can be given a quick test for nitrates. A few drops of test solution on a split stalk turn deep blue when high levels of nitrate are present.
Most MU Extension county offices have test kits to provide quick nitrate checks. This test gives only rough indications of potential problems. It's a warning.
A more accurate, quantitative test must be done in a laboratory, but that takes time. The lab test works best on stored forages such as bales, balage or silage.
On the teleconference, a regional specialist asked Kallenbach about corn being chopped and fed to cow herds. That is being done already in dry areas of southern Missouri.
"That works well—if it is done quickly," Kallenbach said.
The worst thing is to chop a load of cornstalks, then let the forage sit on the feed wagon overnight. In that time, the deadly nitrates convert into even deadlier nitrites.