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KSU clinical veterinary toxicologist discusses drought-related forage issues

by Wyoming Livestock Roundup

During a Kansas State University (KSU) Beef Cattle Institute Cattle Chat podcast on Aug. 5, KSU Clinical Veterinary Toxicologist Steve Ensley discusses drought related plant issues as parts of the U.S. experience dry conditions. 

Common plant issues 

Hydrogen cyanide, sometimes called prussic acid, is a toxin commonly forming in Johnsongrass which can be a problem for producers across the country. 

“Cyanide and nitrate are toxins producers have a lot of concerns about and see issues with depending on the weather and environment,” shares Ensley. “Prussic acid is a cyanide toxicosis which is very acute – animals begin to show signs within 30 minutes of consuming plants with high levels of cyanide.” 

Animals typically have a hard time breathing, experience spasms, foam at the mouth and die quickly. 

“The good thing about cyanide and nitrate is it’s very quick,” he notes. “It can be very acute and if producers can get livestock away from the feed source, death loss can be minimal.” 

Commonly seen in the fall after the first frost, nitrates and cyanide are a concern when plants are stressed. 

“A majority of the calls I get are around frost time with producers asking when is it okay to feed,” says Ensley.

He shares, a rule of thumb with forage testing high for prussic acid is, if a producer green chops and feeds it immediately, livestock will be alright. 

“The issue usually happens when producers green chop and leave forage in the wagon to feed the next day – during this time is when their will be a maximum production of cyanide – and that’s when producers can kill the most animals,” he explains. “It’s fairly potent and acute, and treatment options are very limited.”

Grazing considerations 

Livestock are at higher risk of being impacted by cyanide during drought.

“Any time a plant is stressed and cyanide or nitrate is there, it’s always going to cause more of a problem,” he notes. “The biggest problem with cyanide is when there is regrowth after grazing – those sucker feeders, or small plants that come up and grow in the field after grazing, usually have the most concentrate of prussic acid.” 

Initial grazing is typically okay, but when there is a foot tall regrowth – this is when the cyanide concentrates in the plant can really be an issue. If grass is showing signs of yellow ends, this is an indicator of stress. 

Ensley encourages producers to be aware of the current conditions in their pastures before they let cattle out to graze.

“It’s never a good idea to put cattle out and see what happens,” he mentions. 

Haying stressed grasses

Producers have the option to bale stressed forages into hay, Ensley says. 

“When producers bale forage with a high concentrate of cyanide and mechanically crimp it, this will help get rid of a lot of the cyanide in there,” he explains. “Baling forage with high levels of nitrates will help some, but the best way is to silage it.” 

Ensiling forages can decrease nitrate levels by one-third, he mentions. 

“Harvesting can decrease it some, but ensiling will be the best way,” Ensley shares. “If producers want to make hay, they can go ahead, but they will want to make sure to do some testing before they feed it to livestock.” 

In many cases, the only way a producer might know these toxins are there is when cattle start to die. Ensley encourages producers to take a venous blood sample when cattle are starting to show symptoms. 

“If an animal’s blood is chocolate brown, it indicates high levels of nitrate, and if it’s cherry red, this means high levels of cyanide,” he explains. “Being able to look at a venous blood sample is pretty diagnostic – it’s one of the few things done in the field immediately to tell what is going on.” 

The main treatment is to get livestock away from the infected feed source.

“Unfortunately, the U.S. Food and Drug Administration is really limited on antidotes for animals in the last 10 to 15 years,” he mentions. “The same antidotes available 40 years ago are not available now – veterinarians are limited on what they can legally use to treat these illnesses.” 

To listen to the full podcast, visit

Brittany Gunn is the editor of the Wyoming Livestock Roundup. Send comments on this article to 

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