Livestock producers can quickly lose animals if they fail to monitor drought-stricken forages for high levels of prussic acid and nitrate, warns the head toxicologist at the Texas Veterinary Medical Diagnostic Lab (TVMDL).

Johnsongrass can become especially lethal during a drought, says Tam Garland.

“Typically, we tend to see high levels of prussic acid in johnsongrass when we get hot weather or dry signs, or when dry johnsongrass is exposed to a little moisture and grows very quickly,” says Garland. “Prussic acid may also be high when johnsongrass is exposed to frost.”

Producers should beware when they see a ribbon-like appearance to johnsongrass leaves, she says.

“That’s a huge indicator it’s under drought stress and may be hot with prussic acid.”

Any of the sorghum species, such as Haygrazer, sorghum-sudan and some milo, may also contain high levels of prussic acid.

High nitrate levels can be a problem in sorghum hybrids, corn and grain sorghum, silverleaf nightshade and pigweed. Livestock producers can take several precautions, says Garland.

First, test all forages for high levels of prussic acid and nitrate. Each plant sample should include 10-12 plants, which should be randomly selected from a field. Cut samples about 3-4” above the ground. For a large field, divide the land into manageable sections. Label each sample according to the section from which it was taken, and include that information on the paperwork that accompanies the samples.

Fold the samples, if necessary, and place them in a garbage bag (which should be tied tightly) or a large zip-lock baggie. Next, box up the bags with cool packs and send them by overnight courier to the TVMDL at 1 Sippel Road, College Station,TX 77843. Samples must arrive within 24 hours after they’re cut. Garland suggests cutting samples at 3 p.m. and sending them with the last daily shipment.

Garland also advises producers to probe any hay that has recently been baled, if it wasn’t tested before baling. Take three or four probes, put the individual samples into a glass canning jar, and submit them to the lab for testing. Be sure to label the jars if the samples represent hay from separate fields.

“If a round bale shows prussic acid levels, let the bale cure for 30 days, reprobe and retest it,” she says. “Or, roll out the bale and air it out for five days, then rebale the hay.”

Additionally, isolate livestock from suspected plants, including any that may grow on the other side of a fence or along a right of way. Also take caution when moving cattle from one pasture to another. Tightly control their grazing, and consider supplementing – or replacing grazing entirely – with dry hay.

“This is especially true when forage-test values for prussic acid are dangerously high. Finally, be prepared to quickly treat animals that have ingested forage with high levels of prussic acid or nitrate. Treatment generally must take place within minutes to save an animal.”

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