Role of placental function in mediating conceptus growth and survival2

Abstract

Conceptus mortality is a significant factor limiting reproductive efficiency of livestock. In both singlet(i.e., cattle) and litter(i.e., pigs and sheep) bearing species, investigations of conceptus mortality have focused on the period immediately preceding and throughout the attachment phase, around the time of maternal recognition of pregnancy. Recently, data have emerged leading to the suggestion that conceptus loss later in gestation is also significant and that variation in placental size and function may play a very important part in determining whether a conceptus survives. In the pig, the number of conceptuses present after the initial period of loss that survive to term appears to be influenced by the total amount of placental mass present, such that litters containing individuals with relatively small placentae have a greater potential for a large litter size when compared with litters containing similar numbers of individuals with relatively large placentae. In ruminants, recent evidence supports the time of placental development and initial vasculari