Yellow and white sweet clover seems to be everywhere this year. Timely rainfall has sweet clover growing in road ditches, fallow areas, pasture and range, and in places that no one has ever seen it before.
Sweet clover comes from Eurasia and is found from central Europe to Tibet. The first report of sweet clover growing in what would become the U.S traces back to 1739. Since then, it has become naturalized across the continent, but it is common in the Great Plains states.
“Yellow and white sweet clovers are biennials, meaning that it takes them two years to complete their life cycle,” says James Rogers, North Dakota State University Extension forage systems specialist. “Sweet clover will re-seed itself naturally, with seeds remaining viable in the soil bank for up to 40 years.”
The plants we see now that are flowering are second-year plants that will set seed and then die. New seedlings will remain vegetative the first year, developing a deep taproot and a crown with buds that will produce multiple branches in the second year of growth. There are some annual forms of sweet clover, but these are rare.
“Sweet clover has long been recognized as a soil-improving crop with a number of desirable characteristics,” says Rogers. “It is a legume, capable of nitrogen fixation. It forms a deep soil-penetrating taproot that aids in water infiltration and aeration. Sweet clover also tolerates alkaline soils, which makes it an attractive option to include in seeding mixture for alkaline land reclamation. It also has many wildlife benefits, providing food, cover and nesting habitat.”
As with all forage species, sweet clover also has some negative characteristics, Rogers adds. It does not tolerate close grazing or haying in its first year of growth. It can cause bloat. Most notably, it contains coumarin that gives the plant a distinctive sweet odor when crushed but also creates a bitter taste and can reduce palatability to livestock. Overtime livestock can adjust to the taste.
When sweet clover is harvested as part of a hay crop and is not dried properly for baling, overheating can occur within the bale, creating fungi that can convert the coumarin to dicoumarol. Dicoumarol reduces the blood clotting ability of animals that are consuming the forage, which can lead to internal hemorrhaging. The issue can be difficult to detect, as it may take several days for symptoms to develop.
“When feeding hay containing sweet clover, watch for muscle stiffness or lameness or hematomas (swelling under the skin), as this could be an initial indication of sweet clover poisoning,” says Karl Hoppe, NDSU Extension livestock systems specialist. “Cattle tend to be more affected than sheep or horses, which have more selective eating habits than cattle.”
Feeding cattle hay with extremely high concentrations of dicoumarol can lead to death within a day.
Hay that contains sweet clover should be thoroughly cured and stored to avoid development of mold. As it reaches maturity, sweet clover develops thick, coarse stems, which makes drying difficult. When harvesting for hay, use a mower conditioner that will crush the stems to improve drying. Pure stands of sweet clover will be the highest risk for dicoumarol due to the lack of a dilution factor from other species.
“Because of the abundance of sweet clover this year it will be difficult to avoid producing hay with at least some sweet clover presence,” says Hoppe. “If properly baled and stored, dicoumarol development should not be an issue.”
Low-coumarin varieties of sweet-clover have been released, but caution still is advised.
Feeding management can reduce the risk of feeding hay containing sweet clover. Options include blending hay containing sweet clover with other hays to dilute the dicoumarol or using an alternating feeding schedule. Feed sweet clover laced hay for two days followed by hay without sweet clover for three to four days.
Avoid feeding hay containing sweet clover for at least 30 days prior to animals being castrated or dehorned to avoid hemorrhaging issues. Also avoid feeding sweet clover hay to pregnant cows one to two months before calving.
Do not feed moldy hay containing sweet clover to livestock, and do not rely on visual observation to determine toxicity. Even small amounts of mold can result in toxicity. NDSU Extension specialists recommend that ranchers test all hay that contains sweet clover for the presence of dicoumarol. Testing for dicoumarol concentration in hay is available at the NDSU Veterinary Diagnostic Laboratory.
“Sweet clover has become a naturalized part of our pastures and range,” says Rogers. “It provides many benefits to the soil and wildlife and is an excellent forage. It does have some disadvantages, but they can be managed. Proper curing and testing of hay containing sweet clover, as well as proper feeding management, can overcome potential issues.”