A lush field of summer annuals often is a welcome site for cattle producers, but it also poses a threat to beef cattle. Farmers need to pay close attention to when and how much of these forages are grazed to avoid toxicity.
Patrick Davis, University of Missouri Extension regional livestock field specialist, says summer annuals are an important part of the cattle operation grazing rotation. However, these forages can not only reduce productivity, but also profitability of a beef cattle operation. The delineating factor — toxicity.
“Prussic acid poisoning is a potential problem when grazing summer annuals such as sudangrass, sudangrass hybrids or sorghum,” Davis says.
Prussic acid poisoning stops oxygen utilization at the cellular level and, if not treated, results in death. Early symptoms of this toxicity include rapid and labored breathing, frothing at the mouth, ataxia, dilated pupils, muscle tremors and convulsions.
Davis says treatments should include intravenous administration of a mixture of 1 milliliter of 20% sodium nitrite and 3 milliliters of 20% sodium thiosulfate per 100 pounds of body weight. Beef producers also should administer 1 gallon of vinegar in 3 to 5 gallons of water via stomach tube.
Davis says prussic acid poisoning could be prevented. He recommends that farmers do not turn hungry cattle into a potentially toxic field. Instead, graze these forages at heights greater than 20 to 24 inches and wait seven to 14 days after a drought-ending rain before grazing.
Too many nitrates
Nitrate poisoning also is a potential problem with grazing summer annuals, Davis says. Certain weeds, corn, sudangrass, sudangrass hybrids, sorghum and pearl millet all can lead to toxicity in cattle.
This problem occurs when the plant continues nitrate uptake when plant growth is limited by factors such as drought, he explains. Excess nitrate accumulates in the lower portion of the stalk. When cattle consume excess nitrate, it is converted to nitrite instead of ammonia and enters the bloodstream.
Nitrite is very toxic and, if left untreated, leads to animal death, Davis adds. Some nitrate toxicity symptoms include painful rapid breathing, muscle tremors, weakness, incoordination, diarrhea, frequent urination, chocolate-colored blood and overall animal collapse.
Treatment for nitrate toxicity is intravenous solution of a 1% solution of methylene blue. However, like prussic acid poisoning, death is the common first symptom that cattle producers notice, so Davis urges prevention as the best treatment.
Ways to prevent nitrate poisoning include testing potential toxic forages, never turning hungry cattle into potential toxic fields, slowly adapting cattle to potential toxic fields, and diluting toxic forage consumption by providing corn supplementation. Also, these forages tend to be very toxic after a drought, so producers should wait 14 days after a drought-ending rain to graze these forages.
In both cases, treatment requires veterinarian help, so Davis urges cattle producers to discuss potential treatments and prevention techniques with a local large animal veterinarian.