As many of you have already noticed, the wet, cool weather has allowed for the yellow sweetclover to explode this year, especially in brome waterways and brome pastures.
We have received several calls and questions regarding the safety of haying and grazing the sweetclover. There are no definite answers regarding sweetclover, but there are some generalities that usually hold true.
Grazing sweetclover usually does not cause problems, as long as there is grass to graze along with it. If cattle are selectively picking out the sweetclover and not eating much else, there could be the potential for it to cause bloat, similar to grazing alfalfa, but usually cattle eat it along with other grass, so it normally does not cause a problem for grazing animals.
When sweetclover is swathed and baled, it can potentially cause more trouble than just grazing. Sweetclover contains the compound coumarol, which can be converted to dicoumarol in the presence of mold. Dicoumarol is a blood thinning compound, similar to Warfarin, and can inhibit blood from clotting. So if brome and sweetclover are baled together, the presence of mold in the bales can cause dicoumarol to form in the hay. If ingested in high enough amounts, death, abortions, or bleeding problems can occur.
Putting up hay with sweetclover in it can be difficult, because the sweetclover will not dry down at the same rate as the brome or grass that is with it, leading to wet sweetclover and then moldy sweetclover in the bales. As little as 10 parts per million of dicoumarol can cause problems, but testing is difficult because the mold will probably not be consistent in a bale, or even present in some bales at all.
If you are worried about sweetclover in your bales, testing is an option, but it is more effective to try to manage it, such as alternate feeding bales with sweetclover with bales known to not have any, or a different type of bale, such as a forage sorghum bale. Additionally, if you grind feed, try to dilute the possibly contaminated hay with hay that is free of sweetclover, or silage, to help limit the dose that each animal may receive.
Finally, using discretion about when to feed hay with sweetclover is important. If castration or dehorning needs to occur, do not feed any hay with sweetclover for at least 3 weeks prior to the event. The same goes with calving. Because there is the risk of some bleeding around calving, hay with sweetclover should not be fed for three weeks before the anticipated start of calving and during the entire calving period.