Livestock producers can quickly lose animals if they fail to carefully monitor forages as the Texas drought continues, according to a toxicology expert from the Texas Veterinary Medical Diagnostic Laboratory. Dr. Tam Garland, head of the toxicology section, said producers should look for high levels of prussic acid and nitrate that can build up in drought-stressed forages. Testing is the best way to monitor for these conditions.
Johnsongrass can become especially lethal during a drought, she said. “Typically, we tend to see high levels of prussic acid in johnsongrass when we get hot weather or dry signs,” she said, “or when dry johnsongrass is exposed to a little moisture and grows very quickly. 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 said. “That’s a huge indicator it’s under drought stress and may be hot with prussic acid,” Garland said.
Any of the sorghum species – such as haygrazer, sorghum sudan and some milo – may also contain high levels of prussic acid, she said. Nitrate levels in forages are also a concern, Garland said. Sorghum hybrids, corn and grain sorghum may contain high levels, as may silverleaf nightshade and pigweed or careless weed.
Livestock producers can take several precautions, Garland said. First, producers should test all forages for high levels of prussic acid and nitrate. Each plant sample should include 10 to 12 plants, which should be randomly selected from a field. Cut samples about 3 to 4 inches 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 into a large zip-lock baggie. Next, box up the bags with cool packs and send them by an overnight courier to the TVMDL laboratory at 1 Sippel Road, College Station,Texas 77843.
Samples must arrive within 24 hours after they are 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 was not tested before baling. “Take three or four probes, put those individual samples into a glass canning jar, and submit them to the lab for testing,” she said. Be sure to label the jars if the samples represent hay from separate fields.
"If a round bale shows high levels of prussic acid levels," Garland said, "let the bale cure for 30 days, re-probe it and re-test it. Or, roll out the bale and air it out for five days, then re-bale the hay."
Additionally, producers should isolate their livestock from suspected plants, Garland said, including any that may grow on the other side of a fence or along a right-of-way. Farmers and ranchers should also take caution when moving cattle from one pasture to another. Concerned producers should tightly control their livestocks' grazing, Garland said, and should consider supplementing – or replacing grazing entirely – with dry hay.
"This is especially true when forage test values for prussic acid are dangerously high," Garland said. "Finally, producers should 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."
For sample submission instructions, visit http://tvmdl.tamu.edu/services_offered/forms/index_forms.php . For more information about the Texas Veterinary Medical Diagnostic Laboratory visit http://tvmdl.tamu.edu/ .