Iowa Livestock Feeders Need To Watch Nitrate, Aflatoxin Levels

Two potential problems to keep an eye on this fall are nitrates in cornstalks and aflatoxin in corn grain.

Published on: Oct 9, 2012

With forage supplies tight and hay high-priced due to drought in 2012, more cornstalks are being harvested to feed to cattle. In drought years, nitrate tends to accumulate in corn plants and result in higher-than-normal levels of nitrate in corn stover. Nitrate concentrations could be high enough to be harmful to cattle either grazing the stalks or being fed baled stalks.

How big of an issue is this? "It's not a major concern but it's something we need to continue to watch as we go through harvest this fall," says Dan Loy, an Iowa State University Extension beef specialist and director of the Iowa Beef Center at ISU. "We are kind of in uncharted territory. Producers had to feed some of their hay early to get cattle through summer as pastures dried up. Hay supplies will run short this winter to maintain beef cow herds and for feedlots needing a roughage source. Thus, farmers are harvesting more corn stover than usual for feed and forage for cattle."

CAUTION: Iowa producers need to monitor cattle grazing cornstalks this fall for possible nitrate problems. Also, aflatoxin in corn grain can be an issue for livestock feeders in areas struck by 2012 summer drought.
CAUTION: Iowa producers need to monitor cattle grazing cornstalks this fall for possible nitrate problems. Also, aflatoxin in corn grain can be an issue for livestock feeders in areas struck by 2012 summer drought.

ISU Extension specialists can use quick test for nitrate in stover

With drought-stressed corn plants, agronomists and toxicologists say if there were nitrates in that cornstalk when it was harvested, the nitrate may still remain in the stover later on. "We don't know at this time how much of an issue this is," says Loy, "but we have our ISU Extension beef specialists equipped with the quick nitrate test they were using on greenchop corn and corn silage in the summer. So we can continue to monitor the stalk situation through the fall and see if nitrate really is a problem."

Why is nitrate a concern in corn stover? If nitrate is present at high enough levels, how does it affect cattle?

When farmers fertilize the corn crop, normally that nitrogen fertilizer gets translocated to the ear to produce protein in the corn kernels. When drought limits the ability for that transfer to happen some of the nitrogen gets concentrated in the stalk in the form of nitrate.

If a nitrate problem in cornstalks shows up, keep in mind it can be managed

The good news is the nitrate concentration would be in the lower part of the stalk and if you are grazing cornstalks that lower part is the very last thing the cows consume, if they eat it at all. "So this potential nitrate problem, if you find it present, can be managed if you know what level of nitrate is present," says Loy. "You can blend this stover with non-nitrate stover or other roughage to feed. To void problems with nitrate, it's just a matter of taking some precautions and watching what transpires."

What are the symptoms cattle have if they consume high levels of nitrate in stalks or silage? At extreme high nitrate levels, the first symptom you might see sometimes is a dead cow. That's not common. But there are concerns with moderate issues such as possible problems with reproduction in cows, for example. "If a cattle producer does have concerns about nitrate in cornstalks I'd encourage them to contact their nutritionist or veterinarian and discuss this," says Loy. "I don't think it's something to be alarmed about, yet it is something to watch as we go through this fall."

Aflatoxin levels in corn are also important to livestock feeders

What about aflatoxin issues in corn grain harvested this fall? "There are spotty areas around the state reporting some aflatoxin in corn," says Loy. "The good news regarding aflatoxin is the level that can be fed to beef cattle, especially finishing cattle, is up to 300 parts per billion or pbb. From the levels I've heard about showing up in Iowa so far, there are very few cases, if any, that have reached that level."

Livestock are usually the market for aflatoxin-infected corn. Livestock can tolerate some level of aflatoxin, but levels above legal limits can cause problems in livestock. Reduced performance, immunosuppression, liver damage and in extreme cases even death can be the result of feeding high levels of aflatoxin.

The federal Food and Drug Administration has approved these aflatoxin levels for safe use: Feedlot cattle—less than 300 ppb; finishing cattle—less than 200 ppb; Breeding cattle and breeding swine—less than 100 ppb; dairy cattle, young cattle or young swine—less than 20 ppb; intended use not known—less than 20 ppb; human food—less than 20 ppb. For mature poultry and sheep the safe level for feeding corn containing aflatoxin is less than 100 parts per billion.

Livestock, especially finishing cattle and feedlot cattle, will be the end user of much of the aflatoxin-infected corn. Caution and management are crucial to ensure that negative results do not occur from feeding this feed.

Test and monitor aflatoxin levels of corn to be fed to livestock

It is recommended that stored corn that has the aspergillus flavus mold present needs to be dried down to less than 14% moisture content to limit mold growth. Also, cool the grain down after drying and use aeration to control grain temperature. Mold inhibitors may also be applied to corn to reduce mold growth.

ISU recommends testing and monitoring aflatoxin levels of corn to be fed to livestock. Testing corn coproducts such as distillers grain is also recommended. If corn has more than 10 parts per billion, most processors such as ethanol plants will reject that load of corn because in the fermentation process the aflatoxin concentrates by a factor of three in the distillers grain. For example, if corn has 10 ppb of aflatoxin, it ends up 30 ppb in distillers grain.

Blending aflatoxin-bearing corn with clean corn at time of feeding can be a good practice to reduce aflatoxin levels in the animals' diet. But remember, if corn has aflatoxin it can't be fed to dairy cattle, notes Loy. Corn that contains aflatoxin can be safely fed to hogs up to 100 parts per billion. It can be fed to feedlot beef cattle up to 300 parts per billion. "Talk to your veterinarian and nutritionist," he advises. "There is a level you don't want to feed to bred cows or reproducing cattle, but for feedlot and finishing cattle, they can use the corn as long as the aflatoxin level isn't too high."

For more information go online and read the ISU Extension publication "Aflatoxins in Corn", PM-1800 Revised August 2012.