The Georgia state government is issuing a warning to horse owners in that state after a shipment of hay imported from Michigan was found to be contaminated with the wild plant known as "hoary alyssum" (Berteroa incana), which is toxic to some horses. The plant grows wild in Minnesota and apparently is difficult to assess in alfalfa bales because it crumbles and mixes with alfalfa dust.
The University of Minnesota has a background paper posted online on the plant and its possible toxic effects. According to that paper, not all horses react to the plant and the range of the plant is supposed to be Minnesota fields, not as far away as Michigan.
About 50 percent of horses have a toxic reaction and develop swollen legs, fever and diarrhea; some go to founder (develop laminitis).
"We have a report of 25 horses sickened from eating alfalfa hay from Michigan that contained this plant. The horses had swollen legs, fever and some were showing signs of foundering," said Commissioner Tommy Irvin of the Georgian Department of Agriculture in a press release warning to horse owners.
"What is especially troubling is that the alfalfa hay looked perfect. The weed was practically invisible in the hay. It was only after close investigation after the horses got sick that the presence of this plant was found," said Irvin.
His advice: "I urge all horse owners in Georgia to check their alfalfa hay and to contact their veterinarian if they see any problems with their horses."