Sweetclover can provide good nutrition to cattle because it is high in protein and energy when not mature, but the biennial legume can become toxic to cattle if fed as hay, according to North Dakota State University (NDSU) extension livestock systems specialist Karl Hoppe.
Sweetclover is a prolific seed producer, because the plant will die after producing seed during the second year, so new sweetclover plants must grow from seed.
Sweetclover grows rapidly, and the best time to make hay from it is early in the growing season, when the plant is short, according to Hoppe, who is based at NDSU’s Carrington Research Extension Center. Sweetclover matures quickly, becoming tall and stemmy. The stem is hard and has low palatability, so cattle will not readily consume it at this stage.
Grazing sweetclover in pastures doesn’t usually cause digestive problems for cattle, although the possibility of bloat can occur, Hoppe added.
When baled too wet, sweetclover contains a substance called coumarin. Mold can grow and convert coumarin into dicoumarol, a blood thinner (anticlotting agent) that will cause hemorrhaging, NDSU said. Simple bruises turn into large hematomas (large bulges underneath the skin that are filled with blood and fluid).
At higher concentrations of dicoumarol in feed, cows can abort, blood can drip from the nostrils and/or sudden death may occur. The toxic effect may last for a month in a pregnant cow even after consuming toxic hay for just a few days, Hoppe noted.
Visual observation of mold in the hay bale is not a good indicator of toxicity. Small amounts of mold can result in toxicity. Testing for dicoumarol concentration in hay is available at veterinary diagnostic laboratories.
When sweetclover haying conditions allow for a quick dry-down with no rain or dew, and hay is stored away from moisture, coumarin does not get converted to dicoumarol, so toxicity should not be an issue, Hoppe said.
“However, weather rarely cooperates, and dicoumarol is usually present,” Hoppe said. “Pure stands of sweetclover are at most risk for toxicity simply because the hay is not diluted with other grasses. The risk also is increased when the plants are mature, because the dense stems make drying difficult.”
Cattle producers should pay close attention to grass hay with some sweetclover present, because sweetclover poisoning may show up unexpectedly. A good rule of thumb is to test all hay that contains sweetclover for dicoumarol content.
According to Hoppe, dilution is the way to feed cattle to avoid sweetclover poisoning. This can be accomplished by mixing the toxic hay with nontoxic hay. The amount of dilution depends on the concentration of dicoumarol and symptoms in the cattle.
Hay also can be fed on an alternating schedule, such as feeding hay containing sweetclover for two days and then going three to four days without feeding sweetclover, Hoppe suggested, adding that producers should not feed sweetclover hay for a month before or during events where bleeding occurs, such as during calving, surgical castration and dehorning.
If sweetclover is ensiled correctly and covered or put up as a baleage, then dicoumaral should not be present, Hoppe said. However, incorrect moisture levels, inadequate packing and failure to cover the sweetclover will lead to molding and toxicity.
Sweetclover can provide good nutrition to cattle when managed properly to control potential toxicities. Testing and knowing the dicoumaral level is critical to managing this feed source safely to prevent poisoning, Hoppe said. Be sure to document the storage location of bale lots containing sweetclover and the dicoumaral levels to prevent poisoning.