Sweet clover isn’t always so sweet
July 21, 2014
It's the smell that earned sweet clover the "sweet" part of its name. But the compound that produces the heady fragrance turns deadly if the plant isn't cured properly.
The compound, coumarin, turns into dicoumarin when sweet clover hay is poorly cured. Dicoumarol is the active ingredient in many rodent poisons, said Dr. Gerald Stokka, extension veterinarian and livestock stewardship specialist at North Dakota State University. Dicoumarol causes blood thinning, which may lead to abortion or death from minor internal or external bleeding.
While sweet clover poisoning may not show up until the hay is fed in the middle of winter, the time to avoid it completely is now, when the sweet smell of coumarin is still in the air.
If sweet clover is harvested in the bud stage, quality is higher than when the plant is in full bloom, said Ken Olson, extension beef specialist with South Dakota State University. As the plant grows and becomes woodier, the crude protein and palatability decline, and the plant requires a longer cure time for the thicker stems.
The cure time is where the danger lies. In wet years, like this one, producers may be tempted to put up hay that isn't quite as dry as it should be. Stokka recommends putting it up at no higher than 16 percent moisture content, though Olson says he would err on the side of putting it up too dry, and closer to 10 percent.
If the hay is put up too wet, it encourages the growth of mold, which is what converts the coumarin to dicoumarol.
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While hay treatments that allow producers to put up hay at higher moisture contents can help solve one problem—that of heat damage to the hay—they probably won't have a significant affect on mold growth, Olson said, and those treatments shouldn't be relied upon to put up sweet clover hay at higher moisture levels.
Though the consequences of feeding sweet clover hay can be far-reaching, a few management techniques should take care of any problems, Olson said.
"If you've got visible mold, you've got a problem. If it smells musty you've got a problem. Those would be your main indicators." While mold you can see or smell is a definite indicator of the potential presence of dicoumarin, it can exist without any outside evidence. Some veterinary diagnostic labs offer tests for dicoumarin in hay, and Olson suggests talking to the local extension agent or the state diagnostic lab to find out if that's necessary and how to go about it.
"If you are concerned the sweet clover hay may have molded you might want to take some preventative measures," he said. Those preventative measures include alternating a few days of sweet clover hay with a few days of another type of hay. "If you feed sweet clover hay exclusively, the dicoumerin will accumulate in their systems and start causing problems," he said.
Olson also recommended grinding sweet clover hay with another type of hay to reduce the amount of sweet clover the animals have access to.
Stokka said sweet clover poisoning was a bigger problem when sweet clover was grown for a nitrogen-fixing crop, and hayed in a field. Most of the sweet clover that becomes hay now is grown in ditch or meadow situations, so is blended with other grasses and forbs. This hay is less likely to cause poisoning because the other plants dilute the sweet clover concentration.
Sweet clover poisoning may be difficult to diagnose, but producers should be on the lookout for swelling in the lower extremities, which may indicate blood pooling there, stiffness, unwillingness to move, abortion, stillborn calves, excessive bleeding from minor wounds, swelling over bruises, black, tarry manure and bloody milk.
Stokka said the first, most important step is to remove the animals from the sweet clover source, then to administer a vitamin K injection, as prescribed by a veterinarian.
While putting up and feeding sweet clover hay requires special care, grazing sweet clover pastures should warrant some additional consideration as well.
Sweet clover can cause bloat similar to alfalfa bloat. Bloat happens when the animal can't get rid of the excess gas that builds up in its stomach. Legumes can produce tiny bubbles in the animal's rumen that can't be belched out, like larger bubbles can. The gas continues to build until the animal has breathing difficulty and sometimes dies.
Stokka suggests feeding a surfactant, or providing a mineral that includes a surfactant, which allows the tiny bubbles to consolidate into bigger bubbles that the animal can expel, when turning animals out in an immature clover pasture. Olson says it's also important to reduce the amount of potassium in the mineral supplement in the early spring, because the plants contain high levels of potassium, putting their systems out of balance and contributing to bloat.
The potential for bloat diminishes as the sweet clover matures, so at this point in the growing season in South Dakota, most danger of bloat is past, Olson said. Because of the late, cool spring and the prolonged growing season, Stokka said there may still be some cause for caution in North Dakota.
Another health issue to watch for in a sweet clover year is eye problems, Olson said. As the clover gets taller and woodier, it becomes less palatable, so the cattle search out the grass that is growing at the base of the sweet clover plants. In doing so, the woody stems may irritate the eyes. If pinkeye is present in the herd, the disease may spread from one cow to another just by walking through the same patch of clover.