Drought-Stressed Crops May Be Toxic
Tuesday, August 7, 2012
Some areas of the Midwest are already seeing problems with high nitrates in drought stressed green chop corn. There are also concerns about blue
green algae toxins and aflatoxins showing up in corn to be harvested later.
Weeds that grow in disturbed areas where grass is suffering may also accumulate nitrates and other toxins that can cause problems in livestock.
Green chop crops should be checked for nitrates immediately and silage tested again after a month.
Nitrates interfere with the blood’s ability to carry oxygen. Depending on the levels of toxins, symptoms can range from lethargy and labored breathing to sudden death. This is a rapidly occurring event and is difficult to treat.
Check out the following links or read below for more detailed information on how to safely utilize drought stressed crops:
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Toxicoses increased in the drought
Geni Wren, Bovine Veterinarian Magazine | August 02, 2012
The 2012 drought has stressed numerous crops and forages, and veterinarians should help their clients be on the lookout for problems caused by toxins in feed.
Steve Ensley, DVM, PhD, Iowa State University, says, “In a three-state area around Iowa we are seeing issues with green chop corn and nitrate toxicosis, corn in general and nitrate toxicosis, blue green algae toxicosis and concerns about aflatoxin in the corn that will be harvested this year."
Ensley says there are weeds that accumulate nitrate in pastures and during drought they are more likely to become an issue because they will grow when grass won’t. “The general rule with potential toxic weeds are they like to grow in disturbed areas of the pasture so look out for areas around feeding areas etc.,” he advises.
If you want to green chop and feed forages immediately like corn or sudan, it is very important to test for nitrates first. If you are ensiling, then you need to test after 1 month of fermentation.
Clinical signs
Nitrate toxicosis interferes with the body’s ability to carry oxygen in the blood, Ensley says. The clinical signs observed are related to how anoxic the animal is. The clinical signs can range from lethargy, to increased resting respiration rate, inability to ambulate to acute death.
Nitrate toxicosis is a rapid occurring event. The dose of nitrate is directly related to how fast death can occur, and Ensley says the antidote for nitrate toxicosis is difficult to obtain.
The Iowa Beef Center’s fact sheet Nitrate Toxicity says a useful rule of thumb is that cattle and sheep can tolerate up to 0.5% nitrate on a dry matter basis. Total nitrate intake, including from drinking water, must be considered. Feeding non-protein nitrogen such as urea does not affect susceptibility to nitrate toxicity. Intake of large amounts of nitrate at one feeding is more likely to produce toxicity than intake of the same levels spread out over several hours.
Livestock can adapt to higher levels of nitrate intake over a period of several days. Inclusion of grain in the diet speeds up the conversion of ammonia to protein and makes ruminants less susceptible to nitrate toxicity.
Nitrate Toxicity fact sheet summary:
- Those who intend to feed drought stressed green-chopped corn from high fertility soils should consider testing, especially if a short period of rapid growth has occurred just prior to harvest.
- Cattle and sheep can tolerate up to 0.5% nitrate on a dry matter basis.
- Cattle and sheep can tolerate more nitrates if feeding occurs over a period of several hours.
- Nitrate tolerance is increased if grain is fed.
- The nitrate levels in the feed and water sources are additive.
- Drought stressed corn should be cut at 12 to 18 inches above the ground level, as the lower stock has the highest concentration of nitrate.
- The ensiling process results in the loss of much of the nitrate and greatly reduces the risk of toxicity.
- Gradually introduce cattle to suspect forages over a period of several days.
For information on how to sample and have drought-damaged corn tested for nitrates, click here.
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Take Precautions When Feeding Drought Damaged Corn as Silage
AMES, Iowa ? When a corn plant is stunted, or not growing normally, nitrates can build up in the plant. Typically, nitrogen that is taken up by the corn plant is converted to amino acids ? the building blocks of protein ? but in the stressed plant this conversion does not occur. And that’s why producers need to know how to handle and feed drought-damaged corn in silage form, according to Steve Ensley, of Iowa State University’s Veterinary Diagnostic and Production Animal Medicine (VDPAM) department.
“The nitrate level can be high enough in stunted plants that if harvested as silage the nitrate can be toxic to livestock that consume the silage,” Ensley said. “The most common problem is when drought stressed corn is green chopped and fed to livestock without going through ensiling.”
Ensiling will lower the amount of nitrate in the plant. Nitrogen availability to the plant, which will depend on recent rain, fertilizer applied and other factors, will affect the level of nitrate in the plant. If producers are planning on making silage from drought damaged corn, the only way they can be sure about the level of nitrate is do some sampling and testing of the corn silage before feeding.
“Producers have several options to help determine whether nitrate toxicity might be a problem,” Ensley said. “Assess the corn field that will be harvested to determine how much of the field has stunted corn that’s not developing a normal ear. Take samples either by taking grab samples of silage cut by a forage chopper or by cutting several entire plants by hand that represent the various types of corn in the field.”
A quick test that will screen for the presence of nitrates in stalks without having to chop the stalk can be done by ISU Extension beef and dairy specialists. A drop of diphenylamine in sulfuric acid on the surface of a stalk split in two will turn a blue-black color if nitrate is present. However, this does not provide a concentration of nitrate. Availability of this screening test varies. In some cases, the screening test may be a part of drought meetings where the beef or dairy field specialists are present.
Other options include getting a representative sample of several stalks and performing a strip test, which can help determine the concentration of nitrate by sending in a sample. ISU Extension beef and dairy specialists also will have capability for this, but due to the time required to prepare the sample for analysis the availability will be more limited than the screening test. Samples also can be sent to commercial feed analysis labs, or your veterinarian can send samples to the Iowa State veterinary diagnostic lab.