Drought-stressed forages: threat to livestock         

[JULY 15, 2005]  URBANA -- Recent rainfall has reduced concerns about nitrate poisoning in cattle, sheep and goats in some areas of the state, but other parts of Illinois may not be so lucky, said a University of Illinois Extension animal systems educator.

"I've been getting a number of calls from producers in southern Illinois who are worried about feeding drought-stressed corn and Sudan grass to livestock," said Dave Fischer, who is based in Edwardsville. "Following adequate rainfall, the ability of the plant to convert nitrates to plant protein resumes, and nitrate levels in the plants return to more normal levels in about five days.

"However, drought-stressed corn and sorghum/Sudan grasses must be managed right to avoid potential nitrate poisoning. Nitrate poisoning interferes with the animal's ability to carry oxygen in the blood, and the animal dies from lack of oxygen. Pregnant animals can also lose a fetus due to lack of oxygen."

Fischer offered some management guidelines for producers to follow.

"Do not graze or feed 'green-chop' corn or Sudan grasses, especially within the first five days following rain," he said. "A good shower on droughty plants will cause the plant to uptake soil nitrates very quickly, and we must allow five days or so for the nitrates to convert to plant protein."

Ensiling the corn or Sudan grass as silage and allowing it to ferment for three to four weeks before starting to feed it can reduce the nitrates approximately 50 percent, he noted. Silage must be ensiled at the proper moisture of 60 percent to 70 percent, depending on the storage structure, in order for proper fermentation and dissipation of the nitrates.

"I prefer to ensile the crop, as opposed to baling, since baling does not significantly reduce the nitrate ions," he said. "If drought-damaged crops are baled or fed green-chop, it is extremely important to test the feedstuffs for nitrate ions before feeding. Properly sample and test the plants, hay, silages for nitrate nitrogen before feeding."

As a general rule, nitrate ion levels should be less than 1,000 parts per million, or 0.44 percent nitrate nitrogen, to be without risk. Levels greater than 4,000 parts per million, or 1.76 percent nitrate ions, should not be fed.

Silo gas, he emphasized, can be dangerous. Even short-term breathing of the nitrogen dioxide gas can injure the lungs and cause sudden death.

"This gas is detected by the bleachlike odor and visible reddish-brown haze," Fischer said. "Since nitrogen dioxide gas is heavier than air, it is seen at the base of the silo chute and on the silage surface. Always run the silo blower for 10 to 15 minutes before entering the upright silo to help ventilate the area and blow off the gas."

The nutritive value of drought-damaged corn or Sudan grass will generally be about 70 percent to 80 percent of normal and can still be a good feed source when the diet is balanced with other energy and protein sources.

"If the producer is going to feed high-nitrate feeds, he or she will need to know what level of nitrate ions is in the feedstuff and limit the amounts fed per day. When fed with other feedstuffs, producers will be able to dilute the total nitrate ions intake to acceptable levels. Avoid feeding high-nitrate feeds to young calves and pregnant animals."

As a rule of thumb, Fischer said, 1,000 parts per million nitrate ions is safe; 1,000-2,000 is generally safe when fed with a balanced diet and limited to one-half of total dry matter to pregnant animals and young calves; at 2,000-4,000, be cautious and limit dry matter intake to less than one-third of diet for non-pregnant animals; and 4,000 parts per million is potentially toxic -- do not feed.

[News release from the University of Illinois College of Agricultural, Consumer and Environmental Sciences]