It depends what clover you are asking about. Sweet clover, yellow clover, or white clover have some potential to cause problems in cattle. These clovers contain a substance called coumarin. When these clovers become spoiled or are damaged, especially when harvested as hay, the coumarin is converted to dicoumarin in a process called sweet clover poisoning. Dicoumarin will interfere with vitamin K metabolism and synthesis. Vitamin K is needed for blood to clot, and when this conversion happens, cattle may experience excessive hemorrhaging. Sweet clover poisoning is highest in moldy sweet clover hay and can occur in cattle fed sweet clover silage. It can also occur when cattle graze sweet clover in a pasture setting, but the pasture setting seems to be the situation where we observe it less frequently.