Prussic Acid Poisoning

             This time of year we always receive calls regarding the safety of Johnson grass for cattle and horses.  Actually, it’s not just Johnson grass producers who need to be concerned with.  Many sorghum and sudan type plants including Johnson grass can release a poisonous substance known as prussic acid or hydrocyanic acid.  This year even though we have had rain, we are still experiencing drought and the stress put on these plants can increase your chances, depending on when and how you turn in your cattle.  There are some losses of cattle almost every year due to grazing on the green plants.  Silage and hay can usually be fed without problems.

 

                The prussic acid content decreases as the plant approaches maturity.  Small plants, young leaves, and tillers are usually the highest in prussic acid.  In other words, the upper leaves will contain more acid than the older lower leaves.

            Drought stricken and second-growth plants are dangerous because they are small and consist largely of leaves, which are high in prussic acid.  Poisoning seems to be less likely to occur if animals eat some grain before they are turned into the pasture.

                The remedy for prussic acid poisoning is an intravenous injection of sodium nitrite and sodium thiosulfate.  However, if cattle are grazing contaminated pastures, death can come quickly.  Therefore, if you have pastures with Johnson grass present, it is advisable to have a sample sent to the TAMU diagnostic lab before taking an unnecessary risk.