When vitamin E, selenium, and other nutrients are supplemented at correct levels and facilities are adequate, many cases of retained placentas cannot be explained. However, the suppression of the immune system at calving and methods to alleviate that suppression may help explain some retention of fetal membranes. In addition, prostaglandin, estrogen, and prolactin production are very low during these critical days. Cortisol is a hormone involved in the body's response to stress and is elevated in cows with milk fever or dystocia. Cortisol powerfully suppresses the immune response.
More research is needed on the effect of immune system suppression on fresh cow performance.
40 mg Copper 3.5 mg 1.6 mg 6 mg Table 2. If blood levels and liver stores are low, deficiencies of these minerals can cause immuno-suppression. Therefore, availability of trace minerals may be important in transition cow performance. One study at the University of Tennessee showed cows which did not receive zinc supplementation had a higher incidence of retained placentas. Because chelated minerals are highly available to the cow, feeding them to periparturient cows may help reduce the occurrence of metabolic disorders.