Protect Livestock From Sweet Clover Disease
By: Gerald Stokka
Improperly curing hay made from certain sweet clover varieties such as white and
yellow sweet clover can cause severe and often fatal hemorrhages in livestock
such as cattle, sheep and goats.
“Unfortunately, proper harvesting can be difficult,” says Gerald Stokka, North
Dakota State University Extension Service livestock stewardship specialist and
veterinarian. “If cutting is delayed until full bloom, the large, high-moisture
stems will take a longer time to dry than the leaves. This will increase leaf
shatter and decrease quality. If baled in early maturity with increased moisture
content, mold growth may develop.”
The problem with sweet clover is that it contains a high level of a unique,
naturally occurring chemical known as coumarin. Mold causes coumarin to be
converted to dicoumarol, which is a potent anticoagulant. Dicoumarol also
interferes with the metabolism of vitamin K, which the body needs for blood
That is a concern to producers because sweet clover is used as livestock feed.
It grows in many annual pastures and can become abundant in years following good
rainfall in the fall.
Cattle consuming affected feed likely will not exhibit symptoms until the
disease becomes severe. At that point, inadequate blood coagulation causes the
animals to become weak and experience an increased heart rate, anemia, bloody
milk and black, tarlike manure.
“Many of these symptoms may go unnoticed, and often extensive internal bruising
is discovered after the animal has died,” Stokka says. “Dicoumarol also has been
shown to cause reproductive disease in cattle.”
Newborn calves are more susceptible to sweet clover disease than older animals
because the calves usually are deficient in vitamin K and unable to protect
themselves from the toxin. In mature animals, toxicity usually occurs after
they’ve consumed 20 to 30 milligrams of dicoumarol per kilogram of hay for
Stokka recommends that producers remove sweet clover from their livestock’s diet
at the first signs of toxicity. In severe cases, administering whole blood
intravenously can resolve hemorrhages and anemia immediately. Administering
injectable vitamin K1 also has been shown to be an effective treatment strategy.
The synthetic vitamin K3 is available in injectable and oral forms, allowing for
easier treatment, but it has not been shown to be effective, Stokka says.
Replacing or blending moldy sweet clover with a high-quality forages will help
avoid the effects of dicoumarol. Also, haylage or silage made from sweet clover
is less likely to have coumarin convert to dicoumarol because anaerobic
conditions necessary for proper ensiling are not conducive to mold growth.
“To be safe, producers should have their sweet clover hay tested to determine
the dicoumarol content,” Stokka advises.
The NDSU Veterinary Diagnostic Laboratory can conduct those tests. For
information on submitting hay samples, contact the lab at (701) 231-7527 or
(701) 231-8307, or visit its website at http://www.vdl.ndsu.edu.
Other methods of reducing the risk of sweet clover disease include:
* Planting sweet clover varieties with low coumarin content
* Curing and drying sweet clover carefully before baling
* Avoiding feeding sweet clover forages in late gestation
* Blending all predominantly sweet clover forages suspected of contamination
with other forages or feeding these forages for only a short time, such as five
to seven days, to avoid the cumulative effects on the animals’ clotting