Hay growers should be aware of possible toxicity issues in legumes and grasses, reminds Mike Murphy, a University of Minnesota veterinarian. For example, yellow or white sweet clover that molds after baling can cause bleeding in cows and calves, he says. Mold converts coumerol, a natural component in sweet clover, to dicumerol, which causes bleeding by reducing clotting factors in the blood, Murphy says. Cows that consume the moldy clover may bleed at calving and have weak calves. Horses can also have bleeding problems. Hay containing sweet clover should be core-sampled to test for dicumerol. Testing can be done at the North Dakota State University Plant Diagnostic Lab, Murphy suggests.
Alfalfa and clovers infested with a mold called Cymodothea trifolii can cause sun sensitivity and liver damage in horses. When the plants are moldy, an unknown toxin causes the liver damage that results in swelling and blistering in light-colored horses exposed to the sun. While black horses may suffer from liver damage, they may not show the tell-tale blistering and swelling signs, Murphy says.
Animals fed clovers infested with the mold Rhizoctonia leguminicola can suffer from a condition known as "slobbers," which causes excessive salivation. The mold is characterized by a black patch on the plants. It normally occurs when the temperature is above 80 degrees and the humidity exceeds 60%. The mold often runs its course in two to four weeks, depending on the weather, he says.
For more information, call the University of Minnesota Veterinary Diagnostic Laboratory at 612-625-8787.