Infection of the uterus during gestation causes hyperemia, which, at calving, interferes with the normal release of the placenta. Infections can also cause fetal death and abortion, which, in turn increases the occurrence of retained placentas. Dystocia, cesarean section, and fetotomy all increase the female's risk of retaining the fetal membranes. Hereditary has been implicated in the incidence of retained placentas. Daughters of dams with retained placentas have a higher rate of retained placentas themselves, and studies have shown a distinct sire effect.
Retained placentas are more common in dairy breeds than in beef breeds.
Beta carotene, iodine, and selenium have all been reported to decrease the incidence of retained placentas when added to the diet. However, the important point to remember is that a balanced ration is essential in preventing reproductive problems of all kinds, but that the addition of an excess of any vitamin or mineral cannot be expected to increase the overall fertility of the herd. There has not been consistent evidence to warrant the addition of excess nutrients to properly balanced rations. No treatment may be required when neither clinical signs of illness nor evidence of metritis accompany the retained placenta. In most cases, manual removal of the placenta is not advised.