Prussic acid poisoning is usually a concern in the fall when animals graze after a frost. However, this type of toxicity can also develop in forages during a drought, and it has recently started to wreak havoc on a few livestock operations in parts of Central Texas.

Oklahoma State University Extension addressing the issue prussic acid is also known as hydrocyanic acid or cyanide and may be deadly if ingested by livestock. The extension veterinarians say this compound can be found in sorghum species, including Johnsongrass, when it is extremely dry, and they advise producers of the risks of grazing cattle in this situation.

Know the signs

If plants are stressed by drought conditions, naturally occurring hydrocyanic glycosides will convert to prussic acid when they are broken down via chewing or mechanical harvest. Then, prussic acid is released in the rumen and absorbed into the bloodstream.

Once in the circulatory system, the toxin prevents cells from taking up oxygen. The clinical signs most often seen include excitement, muscle tremors, increased respiration rate, excess salivation, staggering, convulsions, and collapse. If an animal dies, the cause of death would ultimately be asphyxiation at the cellular level due to a deprivation of oxygen.

Prussic acid poisoning progresses quickly, so it is crucial to remove livestock from a pasture and contact a veterinarian if animals start to display clinical signs. Veterinarians can administer sodium nitrate and sodium thiosulfate to reverse the toxicity, but these drugs can be hard to obtain. Furthermore, treatment will only be successful if it is initiated quickly.

It is advisable to contact your veterinarian before grazing potential toxic plants to make sure your veterinarian will have availability to respond and have the necessary drugs on hand to treat the cattle if a problem arises.

Be proactive

To inhibit prussic acid poisoning, avoid turning cattle out to a pasture on empty stomachs. Provide feed prior to grazing to reduce their consumption of forages containing prussic acid. Also, wait to graze sorghum species until plants are 18 to 24 inches tall, and practice rotational grazing to keep animals from grazing lush growth. Try to change pastures early in the morning rather than later in the day. Cooler mornings temperatures mean less heat stress on forages and cattle.