Retained foetal membranes Foetal membranes are normally expelled in 3-8 hours. However, retained foetal membranes (RFM), are retained for more than 24 hours. Ninety four percent of cows that cleaned within 24 h did so in 12 h. In 50 studies, the median incidence of RFM is 8.6%, ( %). Why does it occur? Maternal immunological recognition of foetal MHC class I proteins –which are expressed by trophoblast cells– triggers an immune/inflammatory response that contributes to placental separation at parturition. When cotyledon-caruncle attachment fails to separate at the right time after delivering the calf, retained placenta occurs. The incidence of retained placenta can be increased by several factors related to management, health and nutrition. Fertility problems in dairy cattle