BASICS
- Sweet clover has erect stems and leaves divided into 3 segments and spikes of flowers, white or yellow, that give off a sweet odor when crushed
- Grows in moist soils throughout the USA and Canada and can reach 1.8–2.4 m (6–8 feet) high
- Sweet clover may be grown for hay or become a weed invading pastures and roadsides
- Ingestion of moldy sweet clover hay interferes with normal blood clotting in horses
- Sweet clovers (Melilotus alba, M. officinalis) and sweet vernal (Anthoxanthum odoratum) contain the nontoxic compound coumarin. When cut and baled for hay under high moisture conditions, various molds (Penicillium spp., Aspergillus spp., and others) metabolize coumarin to form dicoumarol, which leads to bleeding
- Dicoumarol in hay >20 ppm suggests potential toxicity problems; most toxicoses in livestock are reported at levels >30 ppm. Prolonged consumption of moldy hay at 10 ppm can cause clinical signs
- Bleeding diathesis, ranging from mild to severe
- Generally, horses show symptoms within 3–8 weeks after initial ingestion
- Hemorrhage may be internal or external—epistaxis; fecal blood
- Swellings may appear over bony protuberances of the body because of bruising and hematoma formation
- Lameness can result from hemorrhage into joint capsules and soreness may result from muscle hematomas
- Profuse hemorrhage can occur during minor surgical procedures or during parturition
- Symptoms include anemia, pale mucous membranes, weakness, abnormal heartbeat, and death
- Sudden death often is marked by massive hemorrhage into the thorax or abdominal cavity or around the brain
Dicoumarol interferes with normal blood clotting because of a reduction in the concentrations of the active forms of clotting factors II, VII, IX, and X. This results from competitive inhibition between vitamin K epoxide and dicoumarol for the enzyme vitamin K epoxide reductase, which converts inactive vitamin K epoxide back to its active vitamin K form in the body. Thus, dicoumarol causes vitamin K deficiency by inhibiting regeneration of the active form of vitamin K.
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MISCELLANEOUS