Sweet clover, a common forage legume, under certain conditions can cause toxic effects in cattle. The sweet clover plant is high in the compound coumarin, which can convert to a toxic substance called dicoumarin if the plant is spoiled or damaged. Dicoumarin interferes with the metabolism and synthesis of vitamin K and prevents normal blood clotting resulting in hemorrhages and associated symptoms.
University of Nebraska extension literature indicates that preliminary symptoms include stiffness, lameness, dull attitude, and hematomas or blood clots beneath the skin, particularly around the hips, brisket and neck. Mucous membranes can turn pale, indicating anemia. The toxin also can cause reproductive problems at sub-clinical levels.
Moldy sweet clover hay is the typical cause of toxicity. Poisoning occurs less often in silage than in hay and infrequently in pastured animals.
Nebraska extension specialists suggest several management steps to avoid sweet clover toxicity.
- Use caution feeding sweet clover that is spoiled or moldy. Test suspect hay.
- Plant only low-coumarin-content sweet clover (Melilotus dentata). Avoid contamination of pastures or hayfield with yellow (M. olfficinalis) or white (M. albus) sweet clovers, which have high levels of coumarin.
- Stack or bale sweet clover only when it is well cured and dry.
If you suspect hay could be toxic, feed it for seven to 10 days and then replace it with alfalfa or other forage for an equal period of time.
- Do not feed sweet clover for at least two weeks before or during the calving period.