Nutrition and potential toxicity of sweet clover hay
I wrote about sweet clover in pastures last summer, but am returning to the topic of sweet clover again in this column. Today I am going to focus on sweet clover in hay. The yellow flowers on sweet clover made it very apparent in pastures and hay fields throughout the region this past summer. It produced a lot of forage that was baled into hay.
If it was baled before it became too mature, it should contribute to hay with excellent nutritional quality. Unfortunately, there is a dangerous downside in sweet clover hay. If it was put up a little wet so that it molded, it can contain dicoumarol, which is a toxic compound. The growing sweet clover contained coumarin, a harmless compound. Mold fungi convert the safe coumarin to the toxic dicoumarol. Thus, dicoumarol is only a concern in moldy hay. Unfortunately, high levels of sweet clover production this past summer means that windrows were heavy and drying was slow. If hay was put a little wet, mold presence is likely.
If dicoumarol is present, its toxic effect is that it destroys the clotting factor in blood, so animals can have internal bleeding issues. This can lead to lameness, nose bleeds, bloody feces, and in more severe cases, abortion and eventually, bleeding to death.
Now that the hay is already in the bale, the important next step is to determine if dicoumarol is present, and if so, how much. The North Dakota State University Veterinary Diagnostic Laboratory provides a test of hay for dicoumarol level. Contact your veterinarian to submit samples of suspect hay. Once the level is known, then management options can be considered. One option for feeds with low dicoumarol levels is to blend them with feeds that do not have dicoumarol to dilute the feed mixture to a safe level. Another is to switch every other week between the sweet clover hay and alfalfa hay (or another hay without sweet clover). While these approaches lessen the severity of the poisoning, caution is still needed, including close observation for symptoms of poisoning. It will also be important to not feed hay that contains dicoumarol to cows that are near calving or during calving. In the same light, also do not feed dicoumarol-containing hay to calves or other classes of livestock that will undergo surgical procedures, such as castrating or dehorning.
The bottom line is that hay that contains sweet clover can be an excellent feed as long as the dicoumarol level is known and feeding management is used to prevent poisoning.