“Panicgrass” – Fall Panicum toxicosis in horses.
In 2004, our practice was involved in documenting an important toxin for horses—fall Panicum (Panicum dichotomiflorum) grass. This common native grass has been fed to horses in hay and in pasture probably since the Europeans first brought horses to our area. But, while we know that it doesn’t cause illness all the time, certain growing conditions can cause it to become toxic, as it did in Nokesville, VA in 2004. We don’t know what triggers the grass to become toxic, but we do know that it sometimes does become toxic, and the conditions are right this year. This study proved the hepatotoxicity: http://www.ncbi.nlm.nih.gov/m/pubmed/17186859/
Currently, there are several cases of liver disease in Fauquier, Clark and Loudon counties that appear to be from grazing Panicum grass in the pasture. Some signs of toxicity from eating the grasses includes: decreased appetite, lethargy, somnolence (unusual periods of sleepiness), mild colic, or neurological signs. Some horses have no symptoms at all.
If you have this plant in your pasture or if you find it in your hay cut this year, you may want to have your horses tested for liver disease; this involves a simple blood draw. Call us at 703-754-3309 if you would like us to consult on a case you think might be panicum toxicosis, or if you just would like blood work on your horse to be sure. You can also consult your County Extension agent if you need help with plant identification.