August 4 , 2006

 

High nitrates in drought-stressed corn can poison livestock

 

 

Producers seeking alternative feed sources such as heat damaged corn this exceptionally dry US summer may have to be aware of a potential pitfall: these feed sources can be dangerously high in nitrates, a University of Nebraska-Lincoln forage specialist said.

 

High nitrate levels can be found not only in corn forage but other annual grasses, said Bruce Anderson, forage specialist in the university's Institute of Agriculture and Natural Resources

 

When conditions are extremely hot and dry, the metabolism of the corn plant slows down and the plant could not convert the nitrates absorbed from the soil, Anderson said.

 

However, producers can still safely feed livestock from such feed sources if they are aware of proper harvesting and feeding techniques, Anderson said.

 

Nitrates are most abundant in the lower six to eight inches of plant stems. Unless this portion of the plant is grazed or harvested, toxic nitrate levels should not pose a threat. Grazing animals seldom eat the lower portions of plants anyway, Anderson said.

 

When the drought-damaged corn silage is harvested within a few days after a significant rainfall, nitrate problems may result as the plant may take in a "big gulp" through the root system and not have the ability to move it into the kernel.

 

The best option, however, is to control the type and quantity of forage offered to livestock.

 

Producers can also follow simple tips like not allowing the animals to graze when when they are very hungry so they do not eat the bottom six inches of summer annuals, Anderson said.

 

Drought-stressed corn can be harvested for silage or hay and this results in a fairly safe product, Anderson said.

 

The fermentation process can reduce up to half the nitrates in corn cut for silage, Anderson said. However, in order to do that, moisture levels must be reduced to 65 percent to 70 percent before ensiling. Producers also can cut corn and let it dry in the field or mix silage with dry ingredients to take up some of the moisture.

 

Hay should be cut 8 to 12 inches above the ground to avoid the high nitrate levels found in the bottom portion of stems. It also must be allowed to reach appropriate moisture levels before baling to avoid mold growth, Anderson said.

 

Green-chopping is a riskier option. Green chop should be fed immediately after chopping and not allowed to heat up as it causes nitrates to convert to nitrites, which are 10 times as toxic when fed to animals.

 

Always test nitrate levels in the green chop, hay or silage before feeding it to animals, Anderson said.

 

If nitrates is higher than the potentially toxic level, use the feed for only a portion of the total ration, with the rest from lower nitrate sources, Anderson advises.

 

Legume hay such as alfalfa, prairie hay and other perennial grasses and grains all help reduce nitrate levels, Anderson said. Grains are especially effective because they help microbes in the rumen incorporate nitrates into a safer product.

 

Anderson said that producers should never assume their feed is safe and urges them to collect samples and analyse them for nitrates before feeding.

 

Samples can be taken to commercial laboratories for feed analysis, Anderson said.

 

Nitrate poisoning can be fatal and includes symptoms such as laboured breathing, excessive salivation, bloating, tremors and immobility, Anderson said. If nitrate poisoning is suspected, a veterinarian should be contacted immediately.