Sweet Clover Poisoning - Frequently Asked Questions

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 What is sweet clover poisoning?
Sweet clover poisoning is caused when feeding moldy sweet-clover hay or silage that contains dicoumarol. Dicoumarol is a toxic compound that is produced through weathering of a normal component of sweet clover called coumarol. It is the dicoumarol that causes the sweet clover poisoning, preventing normal blood clotting and causing extensive hemorrhaging.

What causes sweet clover poisoning?
When sweet clover becomes spoiled or is improperly cured the coumarol is converted to the toxic substance dicoumarol. This toxin interferes with the metabolism and synthesis of vitamin K. Vitamin K is essential for liver function, necessary to prevent the seepage of blood from the circulatory system and to establish blood clotting. Without vitamin K, the blood will not clot properly after an injury, and this is why sweet clover poisoning is also called sweet clover bleeding disease.

Is all moldy sweet clover toxic?
Not all moldy sweet clover is toxic, and just because no mold is present or visible does not mean that the sweet clover is not toxic. Poisoning occurs less frequently in silage than in hay, and rarely occurs in animals on pasture.

How long does the toxic substance, dicoumarin, remain in sweet clover?
Toxic levels of dicoumarin can remain for 3 to 4 years of storage. Dicoumarin has never been observed in other clovers or alfalfa. If animals have been fed for 3 weeks with no sign or symptoms, it is likely that there is no toxicity present.

What are the signs and symptoms of sweet clover poisoning?
Cattle that suffer from sweet clover poisoning usually behave normally until the problem becomes severe. Under severe conditions animals are very weak, and stiff; reluctant to move because of hemorrhages in joints and muscles. Bloody milk is another sign. Other internal signs, not visible to the naked eye, include increased heart rate, anemia, and extensive internal hemorrhages that are only found after the animal has died from bleeding to death from an accidental or surgical wound.

Is there treatment available for sweet clover poisoning?
Animals that show signs of sweet clover poisoning can sometimes be saved by a direct blood transfusion. It is important to consult with your veterinarian immediately if animals are showing signs of poisoning. Intramuscular administration of vitamin K can also be done, again consult your veterinarian. It is also important to remove all animals from the sweet clover and place them on a high quality alfalfa that is high in vitamin K and in calcium.

What animals are most susceptible?
All animals are susceptible, but younger cattle are more susceptible than mature cows. Although cows may abort or give birth to stillborn calves if they are on a sweet clover ration that is toxic.

How can sweet clover poisoning be prevented?

  • Plant sweet clovers low in coumarol. Make sure the hay is thoroughly dry; this can take more than 14 days because of the course stem and high moisture concentration of sweet clover. An alternative to lengthy curing is to silage the sweet clover, decreasing the chances of toxicity.
  • Feed sweet clover hay or silage for only two weeks at a time, then feed another type of forage for two weeks, then feed sweet clover for another two weeks; two weeks on, two weeks off program. This helps to neutralize the toxicity, intermittent feeding is safer than mixing good hay and moldy hay together.
  • Do not feed sweet clover 3 weeks prior to calving, or before any surgical procedures like dehorning and castration.
  • Supplement with vitamin K, this helps to neutralize toxicity. Supplementing with calcium will help prevent hemorrhaging.
Feeding Legumes to Cattle
Moldy Feed and Reproductive Failure in Cows

Prepared by Nanita Blomquist , Ag-Info Centre, Alberta Agriculture and Rural Development

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This document is maintained by Marie Glover.
This information published to the web on February 26, 2004.
Last Reviewed/Revised on December 19, 2017.