The record setting temperatures of the past week combined with rainfall far below average, has led to drought conditions across Tennessee. Those brown pastures and hayfields are not only lacking in nutritional grasses, but may actually contain some plants that are potentially toxic to livestock. During drought and other times of pasture shortage, animals will eat plants they might otherwise not, and the possibility of consuming toxic plants increases. Plants may be toxic to livestock because they are nitrate accumulators, cyanide (prussic acid) producers, or because of certain chemicals found naturally in the plant such as those in many weeds. Being able to identify what plants can be potential problems is a critical step in keeping livestock healthy during periods of dry weather. In Tennessee soils, application of nitrogen fertilizer is critical to establishing and maintaining a healthy, productive stand of grass. Unfortunately, in certain situations, these nitrates can accumulate in the stems of plants and cause major problems in livestock. Nitrate toxicity is caused by cattle consuming forages that contain higher than normal levels of nitrates or nitrites.
Certain plants have a higher tendency to accumulate nitrates than others. Summer annuals such as sorghum, Sudan grass, and millet normally receive high levels of nitrogen fertilization that contribute to nitrate accumulation. High levels are also frequently found in Bermuda grass. Weeds such as pigweed and ragweed are also prone to accumulate high levels of nitrates. Some plants have especially high levels of cyanide early in their growth phase or have the ability to concentrate high levels during times of stress such as a drought. A drought while the plant is in an active growing stage can cause release of cyanide acid (prussic acid) from its bound state within the plant. Potentially toxic levels can develop in most varieties of Sorghum, Sudan grass, and Johnsongrass.
Finally, many plants contain chemicals which make them toxic to livestock. Weeds such as perilla mint, jimsonweed, and the various nightshades contain toxins that can cause respiratory disease, decreased production, and even death. Animals will normally stay away from these plants if other grasses are available, however during periods of drought when other options are limited, they will often consume amounts that will be harmful. The hot, dry weather experienced recently can be hard on livestock, just as it can be to humans. Take some time to check your pastures and see what plants are there that might be potential problems.
