Sweet clover can provide good nutrition to cattle because it is high in protein and energy when not mature.
However, sweet clover can become toxic to cattle if fed as hay, North Dakota State University Extension livestock systems specialist Karl Hoppe cautions.
Sweet clover is a biennial legume that lives for two years. It is a prolific seed producer because the plant will die after producing seed during the second year. New sweet clover plants must grow from seed.
The wet fall conditions of 2019 in many parts of the state created the perfect conditions for the first year’s growth of sweet clover. As a result, the easily recognizable yellow or white blossoms of sweet clover are a common sight this growing season. Without the blossoms, sweet clover leaves look similar to those of alfalfa, except sweet clover leaves are serrated around the entire leaf edge, whereas alfalfa leaves are only serrated at the tips.
Sweet clover grows rapidly, and the best time to hay 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. Sweet clover 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 sweet clover in pastures doesn’t usually cause digestive problems, although the possibility of bloat can occur.
Sweet clover contains a substance called coumarin. When sweet clover is baled too wet, mould can grow and convert coumarin into dicoumarol. Dicoumarol is a blood thinner (anticlotting agent) and will cause hemorrhaging. Simple bruises turn into large hematomas (large bulges underneath the skin that are filled with blood and fluid).
At higher concentrations of dicoumarol in the 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 feeding toxic hay for just a few days.
Visual observation of mould in the hay bale is not a good indicator of toxicity. Small amounts of mould can result in toxicity. Testing for dicoumarol concentration in hay is available.
When sweet clover 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.
“However, weather rarely co-operates and dicoumarol is usually present,” Hoppe says. “Pure stands of sweet clover 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.”
Producers should pay close attention to grass hay with some sweet clover present because sweet clover poisoning may show up unexpectedly. A good rule of thumb is to test all hay that contains sweet clover for dicoumarol content.
Dilution is the way to feed cattle to avoid sweet clover poisoning. This can be accomplished by mixing the toxic hay with non-toxic hay. The amount of dilution depends on the concentration of dicoumarol and symptoms on the cattle.
Hay also can be fed on an alternating schedule, such as feeding hay containing sweet clover hay for two days, then going three to four days without feeding sweet clover. Don’t feed sweet clover hay for a month before or during events where bleeding occurs, such as during calving, surgical castration and dehorning.
If sweet clover is ensiled correctly and covered or put up as a baleage, then dicoumarol should not be present. However, incorrect moisture levels, inadequate packing and failure to cover the sweet clover will lead to moulding and toxicity.
Sweet clover can provide good nutrition to cattle when managed properly to control potential toxicities. Testing and knowing the dicoumarol level is critical to managing this feed source safely to prevent poisoning. Be sure to document the storage location of bale lots containing sweet clover and the dicoumarol levels to prevent poisoning.