Forages can become deadly in drought conditions

Jul 15, 2011
by DTN

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 cattle.

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 Mc- Millan. 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 cat tle 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 freechoice 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 percent of the ration. — DTN