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DANGEROUS PLANT VARIETIES:
Yellow Sweetclover (Melilotus officinalis)
White Sweetclover (Melilotus alba)
MECHANISM OF TOXICITY:
- Coumarin, a sweet smelling carcinogen once used in perfumes, occurs naturally in sweetclover. It is converted into dicoumarin, an anticoagulant that prevents blood clotting through destruction and suppression of Vitamin K, by fungi during improper curing/drying of sweetclover hay or when the plant is excessively stressed from frosts, drought and maceration.
- Dicoumarin and its chemical derivatives (such as Warfarin) are used in human medicine as blood thinners.
- Dicoumarin is also commonly used in rodenticides (rat and mouse poisons) which, if ingested by any other animal, can cause excessive bleeding and death.
CLINICAL SIGNS:
- Excessive, uncontrolled, spontaneous bleeding (through the nose, mouth or a wound).
- Internal hemorrhaging or external (visible) bruising.
- Upper airway may be compromised due to an expanding hematoma.
- Blood in the feces, urine or milk.
- Stiffness, lameness, weakness, anorexia, pale mucus membranes (anemia from loss of blood cells), increased respiratory rates, rapid/weak pulse, shock, GI hemorrhaging, lesions, intracranial bleeding, stroke, death.
- Death without any visible signs - animals may bleed to death from slight wounds or internal hemorrhages.
- Dicoumarin may pass through the placental membrane and cause hemorrhage in the fetus.
- Often more than one animal is affected at a time.
FIRST AID:
- Remove all moldy, spoiled or damaged hay from the animals.
- Call a veterinarian.
- Once bleeding starts, it may be difficult to save the animal.
- Administer intramuscular injections of Vitamin K1 (menadione). Vitamin K1 therapy requires a minimum of 12-24 hours to be effective, therefore severely affected animals may not survive this time period.
- Direct blood/plasma transfusions from disease-free animals who have not consumed toxic sweetclover may be helpful.
- Calcium supplementation will aid in the prevention of hemorrhage.
- Avoid surgery on animals which have consumed moldy/damaged sweetclover forage.
PREVENTION:
- Carefully examine alfalfa and grass hays (especially brome, but timothy and orchard grass as well) for sweetclover "weeds". Sweetclover is difficult to distinguish from alfalfa. Both have three leaflets per leaf but the margins of alfalfa leaflets are serrated only on the tips; sweetclover leaflets are serrated around their entire edges. When crushed, sweetclover leaves have a distinctive sweet odor. A definitive identification can be obtained from your county's agricultural extension service.
- Do not feed wet/moldy/spoiled sweetclover hay.
- Not all moldy sweetclover is toxic; but the lack of visible mold does not assure that dicoumarin is absent.
- Affected hay may remain toxic for 3-4 years in storage.
- Extra caution must be taken with second year growth, since it contains a higher concentration of toxin.
- Sweetclover poisoning occurs more frequently in hay than in silage.
- Since the toxin can be passed through the milk, discard milk from affected pregnant/nursing mothers.
- Have the hay/feed tested at a state food safety laboratory. Ask for quantitative numerical measurements in parts-per-billion, not subjective interpretations such as "positive" or "negative".
FARM MANAGEMENT:
- Prevent toxicity by curing/drying sweetclover hay properly - allow the stems to dry before baling.
- Avoid putting up wet hay to prevent mold/fungus from forming.
- Avoid the use of large, tightly bound bales.
- Plant only the low coumarin content sweetclovers (Melilotus dentata). Avoid contamination of pastures or hayfield with yellow (M. olfficinalis) or white (M. albus) sweetclover, which contains substantial levels of coumarin.
- Only certified seed can be grown to eliminate the problem of sweetclover bleeding disease. If seed other than certified is sown, it is highly probable that contamination with high-coumarin varieties has occurred. This increases the potential risk of sweetclover bleeding disease.
FACTS ABOUT SWEETCLOVER:
- As with alfalfa, spoilage is very likely to occur in sweetclover hay because the plant's leaves are small, fine and dry quickly, while the stems are thick and retain moisture. Sweetclover hay is often baled/stacked before the stems are fully dry to retain a high proportion of leaves and its color.
- Sweetclover hay is difficult to dry when the days are damp, cool, or short.
- Most of the (di-)coumarin is concentrated in the leaves and flower buds.
- It is often planted in combination with a grass hay such as brome, timothy, or orchard grass. For the first few years the clover will predominate; as the clovers thin out, the grasses take over.
- Like alfalfa, sweetclover is a legume that is prized for its nitrogen-fixing ability.
- It is grown by beef and dairymen as a forage/grazing crop and as a soil builder, and by beekeepers as a nectar source.
- Sweetclover is often used in rotation with corn, cotton or wheat to fertilize the soil, drain/aerate saturated low-lying areas, and suppress weeds.
- Sweetclover is a stemmy plant that grows 2-6 feet high and produces yellow or white flowers. It closely resembles alfalfa.
- Sweetclover is widespread throughout the United States and Canada. Besides its use in agriculture, it grows along roadsides, fence rows, and in old/fallow fields.
REFERENCES:
Overview:
- Yellow/White Sweetclover - Purdue University
- Sweet Clover Poisoning (pdf) - I. A. Schipper, D.V.M.
Plant Identification:
- Sweetclover - University of Pennsylvania
- Yellow sweetclover - University of California
- Cover Crop Database
Medical Details:
- Plant Poisoning, Glycosides - Coumarin
Use as a Rodenticide:
- Warfarin - EXTOXNET
Farm Production and Management:
- Sweetclover Production and Management - North Dakota State University
- Haying FAQ - Ronald Florence
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