Rangeland between Forsyth and Hysham, Mont., shows a bumper crop of yellow sweetclover.

Many noticed it this year throughout Montana and parts of western North Dakota, the exorbitant amount of yellow was pretty hard to miss. Cattle grazed on rangeland that was covered by yellow sweetclover and cowboys trotted horses through it, shocked to notice the sweetclover was saddle horn high in some places. Some producers have even called it “sweetclover in Biblical proportions.”

 “The old-timers would call this a sweetclover year,” stated Dennis Cash, retired Extension Forage Specialist for Montana State University.

Yellow sweetclover is a non-native plant that was introduced into the United States in the early to mid-20th century as a conservation plant, Cash explained. Originally sweetclover was brought in and planted along roadsides and in barrow ditches. Yellow sweetclover is a legume and therefore possesses nitrogen-fixing qualities which can be beneficial for neighboring vegetation. For being a legume, sweetclover is relatively drought tolerant as well. After being introduced, the plant flourished in Montana, especially on the plains east of the Continental Divide.

“Sweetclover’s root system is pretty massive, so it can break up hardpan just like alfalfa can. It’s got some pretty cool characteristics. When they were re-vegetating roadsides, yellow sweetclover was always in the mix,” stated Cash.

Because the plant has some positive attributes, it can’t really be classified as a noxious weed these days, however it is considered invasive. Yellow sweetclover is a biennial, meaning it does not bloom its first year. It will enter dormancy during the cooler months, and then during its second year, the plant will bolt upward, flower and produce seeds before it dies. When moisture conditions are just right, yellow sweetclover can bloom and produce seeds in abundance.

“In ’92 and ’93, we had a couple of wet years back-to-back and those were big sweetclover years too,” Cash said.

Bumper crops of yellow sweetclover are kind of a double edged sword. Cash pointed out that the plant actually does contain some nutritional value and is extremely palatable when the plant is shorter and immature. In fact, researchers out of North Dakota State University found that yearlings gained over two pounds a day on sweetclover pastures. The downside, however, is the fact it is a legume, so yellow sweetclover can cause bloat.

The real issue with sweetclover is when it is made into hay, more specifically, if it is put up wet. Sweetclover contains a compound known as coumarol, which converts to dicoumarol when the sweetclover is moldy or spoiled. Dicoumarol interferes with the metabolism and synthesis of vitamin K in the blood. In short, dicoumarol acts as an anticoagulant.

According to the Merck Veterinary Manual, it takes a concentration of 20-30 milligrams of dicoumarol per kilogram of hay, ingested over several weeks to poison cattle. Cattle can have internal bleeding, but the greater risk is they can hemorrhage after calving, surgery or injury. Dicoumarol can pass through the placenta and newborn calves can also be affected by the toxic agent.

There is no exact timeline when it comes to feeding moldy sweetclover hay because there are so many variables. The Merck Veterinary Manual did allude that pregnant cattle should not be fed spoiled sweetclover hay for a minimum of four weeks prior to parturition.

“If you have some moldy bales, just set them aside, that would be the best thing you could do from a management standpoint,” Cash said.

There is a hay test for dicoumarols which is provided by the North Dakota State University Veterinary Diagnostic Laboratory. It can be somewhat challenging to get an accurate representation of moldy hay, so the laboratory recommends submitting a minimum of 50-100 grams or about 2-4 ounces of forage for testing.

Greater than normal rainfall across the region made it challenging for producers to harvest their first cutting of hay this year. There is a good chance that any sweetclover that was harvested will spoil in the bale, so it is recommend that producers be hyper-vigilant of their hay before feeding it this winter.

“The thing is, we had this wet year with different than normal situations. Moldy hay has some inherent risks. Bad things don’t always happen, but when they do, it’s when these kinds of conditions happen,” Cash explained.

Cash went on to point out, in general, first cutting was harvested late this year, so forage quality could be compromised. He recommends that producers have all of their hay quality tested before feeding. It also wouldn’t be a bad idea to have all hay tested for other mold toxins as well.

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