Nitrate Poisoning Forages Become Deadly in Drought Conditions

Feeding corn stalks, corn hay or corn silage to the herd this year could be
akin to poisoning your cows. Given extreme drought conditions across much of
cattle country, dryland corn crops are more likely to have high levels of
nitrates this year. And the first sign of nitrate poisoning is usually dead
Ken McMillan, Progressive Farmer contributing editor and a veterinarian in
Alabama, says too high of a nitrate load in feed will overload the animal's
bloodstream. The list of symptoms, all related to a lack of oxygen in the
body tissue, is extensive.
"Symptoms include difficulty breathing, convulsions, muddy brown mucous
membranes and blood, drooling, abdominal pain, diarrhea, muscle tremors,
weakness and staggering," says McMillan. He adds that treatment can be
difficult, and often "unrewarding and unsuccessful."
He explains the reason ruminants are sensitive to nitrate levels is basic
biology. "Ruminants convert nitrate to nitrite in the normal rumen digestion
process. Rumen microbes use this nitrogen source to make microbial protein.
High nitrate feed overloads this system and excessive nitrite is absorbed
into the blood. Nitrite converts hemoglobin into methemoglobin that can not
carry oxygen, thus the symptoms, all related to a lack of oxygen."
It's not just corn that will accumulate nitrates at potentially dangerous
levels. Darrell Rankins, a nutritionist with the Alabama Cooperative
Extension System, says other sources include sorghum, sorghum-sudan hybrids,
pearl millet, soybeans, sudan grass, fescue and Bermuda grass. Often the
more common exposures to toxic nitrate levels come from Bermuda grass or
summer annual grasses because they tend to receive high levels of
fertilization. Many weeds also accumulate toxic levels of nitrates,
including pigweed, Canadian thistle, stinging nettle, smartweed, bindweed,
ragweed, lambsquarter, goldenrod and nightshades.
While all of these can present problems to cattlemen, especially in dry
areas, it's the thousands of acres of dryland corn that may cause the
biggest problem moving into this fall. As acres have been lost, producers
will try to salvage what they can for feed. The safest way for cattle to
consume this corn is via grazing. Nitrates are highest in the lower parts of
the stalk, and cows will typically graze the upper stalk, leaves and ears
first. But it's wise to limit grazing times.
This corn can also be green chopped and fed, turned into hay or turned into
silage. Nitrates in stored forages don't degrade much with time. Rankin says
feeding large round bales of hay will increase the possibility of nitrate
toxicity, and free-choice access tends to increase consumption.
There is only one way to protect animals from nitrate poisoning. Rankin says
a laboratory analysis is the only way to insure feed does not contain toxic
levels of nitrates. Most labs will run tests and give results in parts per
million (ppm). On a dry basis, if the nitrate/nitrogen ppm is over 1,500,
there should be limits on the use of the feed source. Anything showing a ppm
over 5,000 should not be used in a free-choice feeding program. In some
cases feeds with these levels of nitrates can be ground up and mixed with
other feed. As a general rule, the nitrate containing feed should make up no
more than 15% of the ration.
Fuente: Dovers


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