August 19, 2002

LINCOLN, Neb. — Feeding drought-stricken soybeans or sorghum as forage requires close management. While they're good sources of needed livestock feed, they also can be toxic, University of Nebraska specialists said.

When used right, the drought-stricken forages are a good substitute for dry pastures, said Bruce Anderson, forage specialist in NU's Institute of Agriculture and Natural Resources.

Harvesting and feeding soybean hay or silage is similar to feeding alfalfa, he said. Harvesting sorghum for forage is similar to harvesting corn and it also can be made into hay or silage.

Feeding these drought-stressed crops is much like feeding other hay crops. Beef, dairy cows and sheep can use the fibrous nature of these drought-damaged plants, while swine can use it more as a filler, Anderson said.

Livestock can graze soybeans, but usually shouldn't graze sorghum because it is too high in prussic acid and nitrates, which are poisonous to cattle, Anderson said.

Soybean silage is best made with a moisture content between 60 percent and 70 percent, Anderson said.

A useful in-field method to test silage moisture is the squeeze test. After chopping some forage, grab a couple of handfuls and squeeze it tightly for about 30 seconds. If it stays in a ball and the palm of the hand is moist, but not dripping wet, it's just right for chopping.

Forage quality drops quickly in soybeans after seed begins to form. It should be harvested before the bottom leaves start to turn yellow, and cut earlier if possible because the stems become woody and poor in quality. It's especially important to harvest before a freeze to prevent leaf loss, Anderson said.

"With soybeans we also have to avoid the loss of leaves," he said. "They crumble easily. We just can't cut them when they start drying, or we'll get sticks."

To aid fermentation in chopped soybean silage, it may be best to mix in chopped soybean plants with corn or sorghum silage, Anderson said. A ration of 1 ton soybean silage to 3 or 4 tons of corn or sorghum silage will improve fermentation of the soybean silage and increase protein content of the corn or sorghum silage by 2 to 3 points.

Soybean producers also could add a silage inoculant designed for legumes like alfalfa and one to two bushels of rolled or ground grain to each ton of silage or add 50 pounds of molasses to each ton of silage.

"In many cases, we'll find these nontraditional hay crops best fed if they are ground and blended with other feedstuffs," Anderson said. "Grinding will help increase consumption and reduces refusal of stems in the feed bunk or hay rack by cattle."

When feeding the silage to livestock, be sure it has gone through its full fermentation cycle to avoid highly toxic nitrites, he said.

Testing the feed for nitrates and quality is key, said Rick Rasby, NU beef specialist. Testing for protein, energy and moisture will allow producers to design a ration that meets the animals' needs.

"Test, mix and blend," he said. "If the forage happens to test high in nitrates then you have to blend it with feeds that are low in nitrates. The easiest way to do that is to grind it and blend it."

Rasby said producers planning to graze drought-stressed fields should fill up the animals with forage or hay before turning them out to graze. If cattle are too hungry, they can eat too much and face nitrate toxicity problems.

When grazing drought damaged forages, do not force cattle to eat the bottom part of the stalk because that's where the nitrites have accumulated.

"You can do this by closely monitoring grazing activity and stocking rate," he said. "Cattle can be adapted to nitrates in feeds, but it must be slowly."

For more information on feeding drought-stressed forages, visit NU's Beef Cattle Production Web site or consult NU Cooperative Extension NebGuides G86-775-A, Prussic Acid Poisoning or G74-170-A, Nitrates in Livestock Feeding on the Web. Both also are available at local Cooperative Extension offices.

08/19/-SA

Bruce Anderson - Ph.D
Agronomy
Professor
(402) 472-6237

Rick Rasby - Ph.D.
Animal Science
Associate Professor
(402) 472-6477

Sandi Alswager Karstens
IANR News and Photography
(402) 472-3030

Department: Agronomy & Horticulture|Animal Science