April 2013 Articles

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Watch for Toxic Plant Problems During Drought

Watch for Toxic Plant Problems During Drought Dr. Jeremy Powell, University of Arkansas With dry, hot weather, late summer pasture can become thin and short. Occasionally, this may entice cattle to browse on weeds that they wouldn’t typically eat with adequate forage available. Some weeds can be very toxic to cattle and other livestock. It never hurts to assess your pasture for toxic plants and realize they can have a detrimental effect on your livestock.Perilla mint weed (aka Purple mint) is very common in our part of the country and is found in semi-shady areas of the pasture. Cattle don’t typically prefer to eat perilla mint weed, but when very little valuable forage is left in a pasture due to drought, cattle may be tempted to munch on this toxic plant. Mint weed contains a ketone toxin that leads to severe respiratory problems in cattle. This toxin causes the affected animal’s lungs to fill with fluid, leaving them unable to breathe. Affected cattle show signs of respiratory distress such as breathing with their mouth open and neck extended, frothy salivation, grunting when breathing and generalized weakness. Death often occurs within one to two days after onset of illness. Treatment for the perilla mint toxin is very limited. Often, the stress of handling the affected animal for treatment is enough to exhaust their already weakened state. The best medicine is to prevent the consumption of the plant. Considered good forage by some producers and a weed by others, johnsongrass can also lead to toxicity problems in cattle. Johnsongrass, sudangrass and other sorghum-sudan hybrids can accumulate nitrates and be a source of nitrate poisoning for grazing livestock. Signs of nitrate toxicity include heavy breathing, staggering, weakness, abortions and death. Johnsongrass can also contain prussic acid (cyanide) in its leaves and stems.. Young plants that have been stressed by drought, frost or recent application of herbicide contain dangerous levels of free cyanide in their leaves. It is especially common in johnsongrass that is less than 18 inches tall and has started to re-grow after a shower following a long dry spell. Cyanide prevents the body’s ability to normally utilize oxygen. Therefore, affected cattle may show respiratory signs, but sudden death is a very common occurrence. Prussic acid will dissipate when johnsongrass is cut and cured for hay. Johnsongrass is very common throughout our state. Dry summer pastures can turn deadly when cattle graze on forages that are poisonous. Usually, the best method of controlling plant toxicity is to limit exposure to the poisonous plant initially. For more information about toxic plants or other tools for managing your farm, contact your county Extension office.