We have had one of the wettest springs I can remember in a long time. Nice little rains keep coming- almost daily. It’s always interesting to see how the spring weather pattern determines which plants will dominate the landscape. This year it seems to be the annual mustards (members of the Brassicaceae family) and Yellow sweet clover (Melilotus officinalis). The color of the flowers are almost identical, but take a closer look and you will notice the flowers are quite different.
The characteristic that will immediately tell you if you are looking at an annual mustard are the long “siliques” that contain the tiny mustard seeds. The siliques resemble very slim green beans.
The Yellow sweet clover, while a non-native , is naturalized throughout much of Wyoming. It is quite picturesque as it lines the highways and byways. The problem is that both mustards and Yellow sweet clover can render hay unpalatable and even toxic to livestock, and with the bumper crops of both this year, ranchers and back yard horse owners need to be aware.
Generally, livestock won’t graze the annual mustards very much, but large amounts of certain mustards can be toxic to sheep and cattle. However, the risk is low. Unfortunately this is not the case for Yellow sweet clover. Grazing of Yellow sweet clover in the field is generally safe, but when put up into hay it can be very toxic.
Yellow sweet clover contains coumarin which is not toxic itself, but if it molds it turns into dicumarol, a potent vitamin K antagonist and anticoagulant. Any method of hay storage that results in molding of Yellow sweet clover can result in deadly amounts of dicumarol in the hay.
If you are feeding hay this winter, make sure to inspect it thoroughly before feeding. If you must feed hay containing Yellow sweet clover, confer with your veterinarian about getting the hay tested and how you can alternate feeds to reduce the chances of toxicity to livestock.