Macon County cattle producers turning herds onto rain-revived pastures this fall should watch for prussic acid poisoning in Johnsongrass and other sorghum species, University of Missouri Extension specialists warn.
Rain after drought can trigger new growth in those plants, and the young shoots, especially the leaves, may hold high concentrations of the compounds that form prussic acid, also called hydrocyanic acid or hydrogen cyanide, according to MU Extension livestock specialist Gene Schmitz.
Frost does not end the risk right away. The National Weather Service has a frost advisory for Macon County from 1 to 9 a.m. Saturday. According to the Extension release, cyanide generally dissipates by gassing off 10 to 14 days after a frost or during the hay curing process.
Tim Evans, MU Extension state specialist in animal health and veterinary toxicology, advises against turning hungry cattle or horses onto pastures with heavy regrowth. He recommends feeding hay or grain before turnout and continuing supplemental feeding of valuable, pregnant animals until the danger passes. Schmitz recommends waiting until plants are about 24 inches tall before grazing.
Signs can appear within five minutes of eating affected forage, and death can follow in as little as 15 minutes, Evans said, though in some cases signs take a few hours. Early signs include rapid or labored breathing that can resemble pneumonia, muscle tremors, excessive salivation, staggering, convulsions, and collapse. Gums may look bright cherry red or bluish, and pregnant cattle can abort.
Evans advises calling a veterinarian as soon as poisoning is suspected, calmly moving all animals to a different pasture or corral, and watching exposed animals for 12 to 24 hours.