Proper grazing management of summer annuals to reduce cattle toxicity

  • Published: Wednesday, June 24, 2020

“Summer annuals are an important part of the cattle operation grazing rotation,” says Patrick Davis MU Extension Regional Livestock Field Specialist.  Therefore, it is important to have proper grazing management to reduce potential toxicity to cattle which can reduce operation productivity and profitability.  Davis will further discuss management considerations to reduce potential cattle toxicity when grazing summer annuals.

“Prussic acid poisoning is a potential problem when grazing summer annuals such as sudangrass, sudangrass hybrids, or sorghum,” says Davis.  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.  Treatments include intravenous administration of a mixture of 1 mL of 20% sodium nitrite and 3 mL of 20% sodium thiosulfate per 100 lb of body weight as well as administering 1 gallon of vinegar in 3–5 gallons of water via stomach tube.  However, Davis urges cattle producers to use prevention since sudden death is often the toxicity symptom cattle producers see.  Prevention recommendations include don’t turn hungry cattle into a potentially toxic field, graze these forages at heights greater than 20 to 24 inches and wait 7 to 14 days after a drought ending rain before grazing. 

“Nitrate poisoning is also a potential problem with grazing summer annuals,” says Davis.  The summer annuals that lead to this toxicity in cattle include weeds, corn, sudangrass, sudangrass hybrids, sorghum and pearl millet.  This problem occurs when the plant continues nitrate uptake when plant growth is limited by factors such as drought.  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.  Some nitrate toxicity symptoms include painful rapid breathing, muscle tremors, weakness, incoordination, diarrhea, frequent urination, chocolate­colored blood and 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 test potential toxic forages, never turn hungry cattle into potential toxic fields, slowly adapt cattle to potential toxic fields, and dilute 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 your local large animal veterinarian.  If you have any other questions related to reducing the incidence of prussic acid and nitrate toxicity in you cattle herd contact myself or your local MU Extension Livestock Field Specialist.      

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